News for general public feed https://home.web.cern.ch/ en CLOUD discovers new way by which aerosols rapidly form and grow at high altitude https://home.web.cern.ch/news/news/physics/cloud-discovers-new-way-which-aerosols-rapidly-form-and-grow-high-altitude <span>CLOUD discovers new way by which aerosols rapidly form and grow at high altitude</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>Aerosol particles can form and grow in Earth’s upper troposphere in an unexpected way, reports the <a href="/news/news/experiments/cloud-discovers-new-way-which-aerosols-rapidly-form-and-grow-high-altitude">CLOUD</a> collaboration in a <a href="https://www.nature.com/articles/s41586-022-04605-4">paper</a><sup>1</sup> published today in Nature. The new mechanism may represent a major source of cloud and ice seed particles in areas of the upper troposphere where ammonia is efficiently transported vertically, such as over the Asian monsoon regions.</p> <p>Aerosol particles are known to generally cool the climate by reflecting sunlight back into space and by making clouds more reflective. However, how new aerosol particles form in the atmosphere remains relatively poorly known.</p> <p>“Newly formed aerosol particles are ubiquitous throughout the upper troposphere, but the vapours and mechanisms that drive the formation of these particles are not well understood,” explains CLOUD spokesperson Jasper Kirkby. “With experiments performed under cold upper tropospheric conditions in CERN’s CLOUD chamber, we uncovered a new mechanism for extremely rapid particle formation and growth involving novel mixtures of vapours.”</p> <p>Using mixtures of sulfuric acid, nitric acid and ammonia vapours in the chamber at atmospheric concentrations, the CLOUD team found that these three compounds form new particles synergistically at rates much faster than those for any combination of two of the compounds. The CLOUD researchers found that the three vapours together form new particles 10–1000 times faster than a sulfuric acid–ammonia mixture, which, from previous CLOUD measurements, was previously considered to be the dominant source of upper tropospheric particles. Once the three-component particles form, they can grow rapidly from the condensation of nitric acid and ammonia alone to sizes where they seed clouds.</p> <p>Moreover, the CLOUD measurements show that these particles are highly efficient at seeding ice crystals, comparable to desert dust particles, which are thought to be the most widespread and effective ice seeds in the atmosphere. When a supercooled cloud droplet freezes, the resulting ice particle will grow at the expense of any unfrozen droplets nearby, so ice has a major influence on cloud microphysical properties and precipitation.</p> <p>The CLOUD researchers went on to feed their measurements into global aerosol models that include vertical transport of ammonia by deep convective clouds. The models showed that, although the particles form locally in ammonia-rich regions of the upper troposphere such as over the Asian monsoon regions, they travel from Asia to North America in just three days via the subtropical jet stream, potentially influencing Earth’s climate on an intercontinental scale.</p> <p>“Our results will improve the reliability of global climate models in accounting for aerosol formation in the upper troposphere and in predicting how the climate will change in the future,” says Kirkby. “Once again, CLOUD is finding that anthropogenic ammonia has a major influence on atmospheric aerosol particles, and our studies are informing policies for future air pollution regulations.”</p> <p>Atmospheric concentrations of sulfuric acid, nitric acid and ammonia were much lower in the pre-industrial era than they are now, and each is likely to follow different concentration trajectories under future air pollution controls. Ammonia in the upper troposphere originates from livestock and fertiliser emissions – which are unregulated at present – and is carried aloft in convective cloud droplets, which release their ammonia upon freezing.</p> <figure role="group" class="align-center"> <img alt="Simulation of aerosol particle formation during the Asian monsoon in a global aerosol model with efficient vertical transport of ammonia into the upper troposphere. Including a mixture of sulfuric acid, nitric acid and ammonia enhances upper-tropospheric" data-entity-type="file" data-entity-uuid="088b9e16-12ca-4680-be95-17b2711bb2fe" height="“auto”" src="/sites/default/files/inline-images/gfabre/Capture%20d%E2%80%99e%CC%81cran%202022-05-19%20a%CC%80%2015.11.18.jpg" width="1845" loading="lazy" /> <figcaption>Simulation of aerosol particle formation during the Asian monsoon in a global aerosol model with efficient vertical transport of ammonia into the upper troposphere. Including a mixture of sulfuric acid, nitric acid and ammonia enhances upper-tropospheric particle number concentrations over the Asian monsoon region by a factor of 3–5 compared with the same model with only sulfuric acid and ammonia. (Image: CLOUD collaboration)</figcaption> </figure> <p>Pictures:<a href="https://cds.cern.ch/record/2806655">https://cds.cern.ch/record/2806655</a></p> <hr /> <p><sup>1</sup>Wang, M. et al. Synergistic HNO3–H2SO4–NH3 upper tropospheric particle formation. Nature, doi:<a href="https://www.nature.com/articles/s41586-022-04605-4">10.1038/s41586-022-04605-4</a> (2022).</p> </div> <span><span lang="" about="/user/31239" typeof="schema:Person" property="schema:name" datatype="">gfabre</span></span> <span>Fri, 05/13/2022 - 09:48</span> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-05-18T15:30:00Z">Wed, 05/18/2022 - 17:30</time> </div> </div> Fri, 13 May 2022 07:48:55 +0000 gfabre 182554 at https://home.web.cern.ch ALICE makes first direct observation of a fundamental effect in particle physics https://home.web.cern.ch/news/news/physics/alice-makes-first-direct-observation-fundamental-effect-particle-physics <span>ALICE makes first direct observation of a fundamental effect in particle physics</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p> </p> <p>The <a href="/science/experiments/alice">ALICE</a> collaboration at the <a href="/science/accelerators/large-hadron-collider">Large Hadron Collider</a> (LHC) has made the first direct observation of the dead-cone effect – a fundamental feature of the theory of the strong force that binds quarks and gluons together into protons, neutrons and, ultimately, all atomic nuclei. In addition to confirming this effect, the observation, reported in a paper published today in <a href="https://www.nature.com/articles/s41586-022-04572-w "><em>Nature</em></a>, provides direct experimental access to the mass of a single charm quark before it is confined inside hadrons.</p> <p>“It has been very challenging to observe the dead cone directly,” says ALICE spokesperson Luciano Musa. “But, by using three years’ worth of data from proton–proton collisions at the LHC and sophisticated data-analysis techniques, we have finally been able to uncover it.”</p> <p>Quarks and gluons, collectively called partons, are produced in particle collisions such as those that take place at the LHC. After their creation, partons undergo a cascade of events called a parton shower, whereby they lose energy by emitting radiation in the form of gluons, which also emit gluons. The radiation pattern of this shower depends on the mass of the gluon-emitting parton and displays a region around the direction of flight of the parton where gluon emission is suppressed – the dead cone<sup>1</sup>.</p> <p>Predicted thirty years ago from the first principles of the theory of the strong force, the dead cone has been indirectly observed at particle colliders. However, it has remained challenging to observe it directly from the parton shower’s radiation pattern. The main reasons for this are that the dead cone can be filled with the particles into which the emitting parton transforms, and that it is difficult to determine the changing direction of the parton throughout the shower process.</p> <p>The ALICE collaboration overcame these challenges by applying state-of-the-art analysis techniques to a large sample of proton–proton collisions at the LHC. These techniques can roll the parton shower back in time from its end-products – the signals left in the ALICE detector by a spray of particles known as a jet. By looking for jets that included a particle containing a charm quark, the researchers were able to identify a jet created by this type of quark and trace back the quark’s entire history of gluon emissions. A comparison between the gluon-emission pattern of the charm quark with that of gluons and practically massless quarks then revealed a dead cone in the charm quark’s pattern.</p> <p>The result also directly exposes the mass of the charm quark, as theory predicts that massless particles do not have corresponding dead cones.</p> <p>“Quark masses are fundamental quantities in particle physics, but they cannot be accessed and measured directly in experiments because, with the exception of the top quark, quarks‌ are confined inside composite particles,” explains ALICE physics coordinator Andrea Dainese. “Our successful technique to directly observe a parton shower’s dead cone may offer a way to measure quark masses.”</p> <figure class="cds-image" id="CERN-GRAPHICS-2022-015-8"><a href="//cds.cern.ch/images/CERN-GRAPHICS-2022-015-8" title="View on CDS"><img alt="Graphics,radiation,dead-cone,gluon,quark,illustration" src="//cds.cern.ch/images/CERN-GRAPHICS-2022-015-8/file?size=large" /></a> <figcaption>As the parton shower proceeds, gluons are emitted at smaller angles and the energy of the quark decreases, resulting in larger dead cones of suppressed gluon emission.<span> (Image: CERN)</span></figcaption></figure> <p><strong>Further information:</strong></p> <ul> <li><a href="https://cds.cern.ch/record/2809214">Additional graphics</a></li> <li>ALICE <a href="/resources/image/experiments/alice-images-gallery">picture gallery</a></li> <li>ALICE <a href="/resources?title=&amp;topic=1117&amp;type=61&amp;audience=All&amp;field_p_resource_display_tags_target_id=ALICE%20%28120%29&amp;date_from=&amp;date_to=">video gallery</a></li> <li>ALICE collaboration: <a href="https://alice.cern/">https://alice.cern/</a></li> </ul> <p> </p> <hr /> <p><sup>1</sup>Technical note: specifically, for an emitter of mass m and energy E, gluon emission is suppressed at angles smaller than the ratio of m and E, relative to the emitter’s direction of motion.</p> <p> </p> </div> <span><span lang="" about="/user/18835" typeof="schema:Person" property="schema:name" datatype="">mailys</span></span> <span>Mon, 05/16/2022 - 12:09</span> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-05-18T15:00:00Z">Wed, 05/18/2022 - 17:00</time> </div> </div> Mon, 16 May 2022 10:09:09 +0000 mailys 182560 at https://home.web.cern.ch Higgs10: The Higgs boson and the rise of the Standard Model of Particle Physics in the 1970s https://home.web.cern.ch/news/news/physics/higgs10-higgs-boson-and-rise-standard-model-particle-physics-1970s <span>Higgs10: The Higgs boson and the rise of the Standard Model of Particle Physics in the 1970s </span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>At the dawn of the 1970s, the idea of a massive scalar boson as the keystone of a unified theoretical model of the weak and electromagnetic interactions had yet to become anchored in a field that was still learning to live with what we now know as the Standard Model of Particle Physics. As the various breakthroughs of the decade gradually consolidated this theoretical framework, the Brout–Englert–Higgs (BEH) field and its boson emerged as the most promising theoretical model to explain the origin of mass.</p> <p>In the 1960s, there were remarkably few citations of the papers by Sheldon Glashow, Abdus Salam and Steven Weinberg on the theory of unified weak and electromagnetic interactions. All that changed, however, in 1971 and 1972 when, in Utrecht, Gerard ’t Hooft and Martinus Veltman (a former CERN staff member) proved that gauge theories employing the Brout-Englert-Higgs mechanism to generate masses for gauge bosons are renormalisable, and hence are mathematically consistent and can be used to make reliable, precise calculations for the weak interactions. This breakthrough was given broad publicity in an influential talk by Benjamin Lee of Fermilab during the ICHEP conference held there in 1972, in which he talked at length about “Higgs fields”.</p> <p>Encouraged, in particular, by the CERN theorists Jacques Prentki and Bruno Zumino, the Gargamelle collaboration prioritised the search for weak neutral current interactions in the CERN neutrino beam, and their representative Paul Musset presented the first direct evidence for them in a seminar at CERN on 19 July 1973. This first experimental support for the unification of the electromagnetic and weak interactions attracted great interest and close scrutiny, but was generally accepted within a few months. The neutral-current discovery convinced physicists that the nascent Standard Model was on the right track. Former CERN Director-General Luciano Maiani, quoted in a <a href="https://cerncourier.com/a/neutral-currents-a-perfect-experimental-discovery/">2013 CERN Courier article</a>, puts it this way: “At the start of the decade, people did not generally believe in a standard theory, even though theory had done everything. The neutral-current signals changed that. From then on, particle physics had to test the standard theory.”</p> <p>The next breakthrough came in 1974, when two experimental groups working in the United States, led by Sam Ting at Brookhaven and Burt Richter at SLAC, discovered a narrow vector resonance, the J/psi, with prominent decays into lepton–antilepton pairs. Many theoretical interpretations were proposed, which we at CERN discussed over the phone in excited midnight seminars with Fred Gilman at SLAC (almost 40 years before Zoom!). The winning interpretation was that the J/psi was a bound state of the charm quark and its antiquark. The existence of this fourth quark had been proposed by James Bjorken and Sheldon Glashow in 1964, and its use to suppress flavour-changing neutral weak interactions had been proposed by Glashow, John Iliopoulos and Maiani in 1970. Mary K. Gaillard (a long-term visiting scientist at CERN), Jon Rosner and Lee wrote an influential paper on the phenomenology of charm in 1974, and experiments gradually fell into line with their predictions, with final confirmation coming in 1976.</p> <p>The attention of most of both the theoretical and experimental communities was then drawn towards the search for the massive W and Z vector bosons responsible for the weak interactions. This motivated the construction of high-energy hadron colliders and led to the discovery of the W and Z bosons at CERN.</p> <p>However, it seemed to Mary K. Gaillard, Dimitri Nanopoulos and myself at CERN that the key question was not the existence of the massive weak vector bosons, but rather that of the scalar Higgs boson that enabled the Standard Model to be physically consistent and mathematically calculable. At the time, the number of papers on the phenomenology of the Higgs boson could be counted on the fingers of one hand, so we set out to describe its phenomenological profile in some detail, covering a wide range of possible masses. Among the production mechanisms we considered was the possible production of the Higgs boson in association with the Z boson, which generated considerable interest in the days of LEP 2. Among the Higgs decay modes we calculated was that into a pair of photons. This distinctive channel is particularly interesting because it is generated by quantum effects (loop diagrams) in the Standard Model.</p> <figure class="cds-image align-right" id="CERN-HOMEWEB-PHO-2022-083-1"><a href="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-083-1" title="View on CDS"><img alt="home.cern,Personalities and History of CERN" src="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-083-1/file?size=large" /></a> <figcaption>Mary K. Gaillard (center), her granddaughter Cleo (left), and John Ellis (right), in 2019, during the celebration of Mary’s 80th birthday.<span>(Image: Berkeley Science Review)</span></figcaption></figure> <p>Despite our conviction that something like the Higgs boson had to exist, our paper ended on a cautionary note that was somewhat tongue-in-cheek: “We apologise to experimentalists for having no idea what is the mass of the Higgs boson … and for not being sure of its couplings to other particles, except that they are probably all very small. For these reasons we do not want to encourage big experimental searches for the Higgs boson, but we do feel that people performing experiments vulnerable to the Higgs boson should know how it may turn up.” This caution was in part because the senior physicists of the day (Dimitri and I were under 30 at the time) regarded the ideas surrounding electroweak symmetry breaking and the Higgs boson with rather jaundiced eyes. Nevertheless, as time went on, the massive W and Z were discovered, the existence or otherwise of the Higgs boson rose up the experimental agenda, and no plausible alternative theoretical suggestions to the existence of something like the Higgs boson emerged. Experimentalists, first at LEP and later at the Tevatron and the LHC, focused increasingly on searches for the Higgs boson as the final building block of the Standard Model, culminating in the discovery on 4 July 2012.</p> </div> <span><span lang="" about="/user/21331" typeof="schema:Person" property="schema:name" datatype="">thortala</span></span> <span>Tue, 05/10/2022 - 16:13</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/john-ellis" hreflang="en">John Ellis</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-05-10T14:09:41Z">Tue, 05/10/2022 - 16:09</time> </div> </div> Tue, 10 May 2022 14:13:16 +0000 thortala 182533 at https://home.web.cern.ch CMS tries out the seesaw https://home.web.cern.ch/news/news/physics/cms-tries-out-seesaw <span>CMS tries out the seesaw</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>The CMS collaboration at the <a href="https://home.cern/science/accelerators/large-hadron-collider">Large Hadron Collider</a> (LHC) has carried out a new test on a model that was developed to explain the tiny mass of neutrinos, electrically neutral particles that change type as they travel through space.</p> <p>In the <a href="https://home.cern/science/physics/standard-model">Standard Model</a> of particle physics, the particles that cannot be broken down into smaller constituents, such as quarks and electrons, gain their mass through their interactions with a fundamental <a href="https://home.cern/science/physics/higgs-boson">field associated with the Higgs boson</a>. The neutrinos are the exception here, however, as this Higgs mechanism cannot explain their mass. Physicists are therefore investigating alternative explanations for the mass of neutrinos.</p> <p>One popular theoretical explanation is a mechanism that pairs up a known light neutrino with a hypothetical heavy neutrino. In this model, the heavier neutrino plays the part of a larger child on a seesaw, lifting the lighter neutrino to give it a small mass. But, for this seesaw model to work, the neutrinos would need to be Majorana particles, that is, their own <a href="https://home.cern/topics/antimatter">antimatter</a> particles.</p> <p>In its recent <a href="http://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/EXO-21-003/index.html">study</a>, the CMS team tested the seesaw model by searching for Majorana neutrinos produced through a specific process, called vector-boson fusion, in data from high-energy collisions at the LHC collected by the CMS detector between 2016 and 2018. If they took place, these collision events would result in two muons (heavier versions of the electron) that had the same electric charge, two ‘jets’ of particles that had a large total mass and were wide apart from one another, and no neutrino.</p> <p>After identifying and subtracting a background of collision events that look almost the same as the sought-after events, the CMS researchers found no signs of Majorana neutrinos in the data. However, they were able to set new bounds on a parameter of the seesaw model that describes the quantum mixing between a known light neutrino and a hypothetical heavy neutrino.</p> <p>The results include bounds that surpass those obtained in previous LHC searches for a heavy Majorana neutrino with a mass larger than 650 billion electronvolts (GeV), and the first direct limits for a heavy Majorana neutrino that has a mass larger than 2 trillion electronvolts (TeV) and up to 25 TeV.</p> <p>With the LHC set to be back in collision mode this summer, after a successful <a href="https://home.cern/news/news/accelerators/large-hadron-collider-restarts">restart</a> on 22 April, the CMS team can look forward to collecting more data and trying out the seesaw again.</p> <p>____</p> <p><em>Find out more on the <a href="https://cms.cern/news/two-ends-seesaw">CMS website</a>.</em></p> </div> <span><span lang="" about="/user/159" typeof="schema:Person" property="schema:name" datatype="">abelchio</span></span> <span>Wed, 05/04/2022 - 10:50</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/ana-lopes" hreflang="en">Ana Lopes</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-05-04T08:42:33Z">Wed, 05/04/2022 - 10:42</time> </div> </div> Wed, 04 May 2022 08:50:30 +0000 abelchio 182484 at https://home.web.cern.ch Higgs10: A boson is born https://home.web.cern.ch/news/news/physics/higgs10-boson-born <span>Higgs10: A boson is born </span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p><strong><em>On 4 July 2012, half a century’s wait came to an end as the ATLAS and CMS experiments announced the discovery of the Higgs boson. </em></strong><a href="https://home.cern/news/news/cern/higgs10-save-date"><strong><em>Celebrate 10 years</em></strong></a><strong><em> since this extraordinary achievement by learning more about the history that led up to it, the next steps in understanding the mysterious particle, and CERN’s role in this endeavour. The “Higgs history” series of Bulletin articles will walk you through this journey, starting with an account by CERN Courier editor, Matthew Chalmers, of the theorisation of the Higgs boson in the 1960s.</em></strong></p> <p><strong><em>_______________</em></strong></p> <p>It’s every theoretical physicist’s dream to conjure a new particle from mathematics and have it observed by an experiment. Few have scaled such heights, let alone had a particle named after them. In the CERN auditorium on 4 July 2012, Peter Higgs wiped a tear from his eye when the ATLAS and CMS results came in. The Higgs boson holds the record (48 years) among elementary particles for the time between prediction and discovery, going from an esoteric technicality to commanding the global spotlight at the world’s most powerful collider.</p> <p>Revealing that the universe is pervaded by a stark “scalar” field responsible for generating the masses of elementary particles was never something Robert Brout and François Englert, and independently Peter Higgs, set out to do. Their short 1964 papers – one by Brout and Englert, two others by Higgs – concerned an important but niche problem of the day. “Of no obvious relevance to physics” was how an editor of <em>Physics Letters</em> is said to have remarked on rejecting one of Higgs’ manuscripts. The papers went from fewer than 50 citations by the turn of the decade to around 18 000 today.</p> <p>At the time the “BEH” mechanism was being dreamt up independently in Brussels and Edinburgh – and in London by Gerald Guralnik, Carl Hagen and Tom Kibble – the Standard Model of particle physics was years away. Physicists were still trying to understand the menagerie of hadrons seen in cosmic-ray and early accelerator experiments, and the nature of the weak force. The success of quantum electrodynamics (QED) in describing electromagnetism drove theorists to seek similar “gauge-invariant” quantum field theories to describe the weak and strong interactions. But the equations ran into a problem: how to make the carriers of these short-range forces massive, and keep the photon of electromagnetism massless, without spoiling the all-important gauge symmetry underpinning QED.</p> <p>It took a phenomenon called spontaneous symmetry breaking, inherent in superconductivity and superfluidity, to break the impasse. In 1960, Yoichiro Nambu showed how the “BCS” theory of superconductivity developed three years earlier by John Bardeen, Leon Cooper and John R. Schrieffer could be used to create masses for elementary particles, and Jeffrey Goldstone brought elementary scalar fields to the party, picturing the vacuum of the universe as a “Mexican hat” in which the lowest-energy state is not at the most symmetrical point at the peak of the hat but in its rim. It was an abstraction too far for soon-to-be CERN Director-General Viki Weisskopf, who is said by Brout to have quipped: “Particle physicists are so desperate these days that they have to borrow from the new things coming up in many-body theory like BCS. Perhaps something will come of it.”</p> <figure class="cds-image align-right" id="CERN-HOMEWEB-PHO-2022-071-2"><a href="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-071-2" title="View on CDS"><img alt="home.cern,Miscellaneous" src="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-071-2/file?size=large" /></a> <figcaption>The 1964 Brout-Englert paper<span> (Image: APS)</span></figcaption></figure> <p>Four years later, Brout, Englert and Higgs added the final piece of the puzzle by showing that a mathematical block called the Goldstone theorem, which had beset initial applications of spontaneous symmetry breaking to particle physics by implying the existence of unobserved massless particles, does not apply to gauge theories such as QED. Unaware that others were on the trail, Higgs sent a short paper on the idea to <em>Physics Letters</em> in July 1964 where it was accepted by Jacques Prentki, the editor based at CERN. In a second paper sent one week later, Higgs demonstrated the mathematics – but it was rejected. Shocked, Higgs sent it to <em>Physical Review Letters</em>, and added crucial material, in particular : “it is worth noting that an essential feature of this type of theory is the prediction of incomplete multiplets of scalar and vector bosons” – a reference to the Higgs boson that was almost never published. In a further twist of fate, Higgs’ second paper was received and accepted the same day (31 August 1964) that <em>Physical Review Letters</em> published Brout and Englert’s similarly titled work. Today, the scalar field that switched on a fraction of a nanosecond after the Big Bang, giving the universe a non-zero “vacuum expectation value”, is generally referred to as the BEH field, while the particle representing the quantum excitation of this field is popularly known as the Higgs boson.</p> <p>In further Nobel-calibre feats, Steven Weinberg incorporated the BEH mechanism into electroweak theory developed also by Abdus Salam and Sheldon Glashow, which predicted the W and Z bosons, and Gerard ‘t Hooft and Martinus Veltman put the unified theory on solid mathematical foundations. The discovery of neutral currents in 1973 in Gargamelle at CERN and of the charm quark at Brookhaven and SLAC in 1974 gave rise to the elecroweak Standard Model. Flushing out and measuring its bosons took three major projects at CERN spanning three decades – the SPS proton-antiproton collider, LEP and the LHC. In the mid-1970s, John Ellis, Mary Gaillard and Dimitri Nanopoulos described how the Higgs boson might reveal itself, and experimentalists accepted the challenge.</p> <p>The discovery of the Higgs boson at the LHC in 2012 ended one journey, but opened another fascinating adventure. Understanding this unique particle will take every last drop of LHC data, in addition to that of a “Higgs factory” that may follow. Is it elementary or composite? Is it alone, or does it have siblings? And what are the roles of the mysterious BEH field in the beginning and the fate of the universe?</p> <p>“We’ve scratched the surface,” said Peter Higgs in 2019. “But we have clearly much more to discover.”</p> </div> <span><span lang="" about="/user/21331" typeof="schema:Person" property="schema:name" datatype="">thortala</span></span> <span>Thu, 04/28/2022 - 11:12</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/matthew-chalmers" hreflang="en">Matthew Chalmers</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-04-28T08:44:44Z">Thu, 04/28/2022 - 10:44</time> </div> </div> Thu, 28 Apr 2022 09:12:16 +0000 thortala 182230 at https://home.web.cern.ch Large Hadron Collider restarts https://home.web.cern.ch/news/news/accelerators/large-hadron-collider-restarts <span>Large Hadron Collider restarts</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>The world’s largest and most powerful particle accelerator has restarted after a break of more than three years for maintenance, consolidation and upgrade work. Today, 22 April, at 12:16 CEST, two beams of protons circulated in opposite directions around the <a href="/science/accelerators/large-hadron-collider">Large Hadron Collider</a>’s 27-kilometre ring at their injection energy of 450 billion electronvolts (450 GeV).</p> <p>“These beams circulated at injection energy and contained a relatively small number of protons. High-intensity, high-energy collisions are a couple of months away,” says the Head of CERN’s Beams department, Rhodri Jones. “But first beams represent the successful restart of the accelerator after all the hard work of the long shutdown.”</p> <p>“The machines and facilities underwent major upgrades during the second long shutdown of CERN’s accelerator complex,” says CERN’s Director for Accelerators and Technology, Mike Lamont. “The LHC itself has undergone an extensive consolidation programme and will now operate at an even higher energy and, thanks to major improvements in the injector complex, it will deliver significantly more data to the upgraded LHC experiments.”</p> <p>Pilot beams circulated in the LHC for a brief period in October 2021. However, the beams that circulated today mark not only the end of the second long shutdown for the LHC but also the beginning of preparations for four years of physics-data taking, which is expected to start this summer.</p> <p>Until then, LHC experts will work around the clock to progressively recommission the machine and safely ramp up the energy and intensity of the beams before delivering collisions to the experiments at a record energy of 13.6 trillion electronvolts (13.6 TeV).</p> <p>This third run of the LHC, called Run 3, will see the machine’s experiments collecting data from collisions not only at a record energy but also in unparalleled numbers. The <a href="/science/experiments/atlas">ATLAS</a> and <a href="/science/experiments/cms">CMS</a> experiments can each expect to receive more collisions during this physics run than in the two previous physics runs combined, while <a href="/science/experiments/lhcb">LHCb</a>, which underwent a complete revamp during the shutdown, can hope to see its collision count increase by a factor of three. Meanwhile, <a href="/science/experiments/alice">ALICE</a>, a specialised detector for studying heavy-ion collisions, can expect a fifty times increase in the total number of recorded ion collisions, thanks to the recent completion of a major upgrade.</p> <p>The unprecedented number of collisions will allow international teams of physicists at CERN and across the world to study the <a href="/science/physics/higgs-boson">Higgs boson</a> in great detail and put the <a href="/science/physics/standard-model">Standard Model</a> of particle physics and its various extensions to the most stringent tests yet.</p> <p>Other things to look forward to in Run 3 include the operation of two new experiments, <a href="/science/experiments/faser">FASER</a> and <a href="/news/news/experiments/cern-approves-new-lhc-experiment">SND@LHC</a>, designed to look for physics beyond the Standard Model; special proton–helium collisions to <a href="/news/news/physics/lhcb-reveals-secret-antimatter-creation-cosmic-collisions">measure</a> how often the antimatter counterparts of protons are produced in these collisions; and collisions involving oxygen ions that will improve physicists’ knowledge of <a href="/news/news/experiments/lhcf-gears-probe-birth-cosmic-ray-showers">cosmic-ray physics</a> and the <a href="/news/series/lhc-physics-ten/recreating-big-bang-matter-earth">quark–gluon plasma</a>, a state of matter that existed shortly after the Big Bang.</p> <p><iframe allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen="" frameborder="0" height="315" src="https://www.youtube.com/embed/J5WYRo17Lls" title="YouTube video player" width="560"></iframe></p> <p paraeid="{f5f764c7-e903-4c0d-8a9e-fcdaf00beb7b}{14}" paraid="1495871037"><strong>Videos:</strong></p> <p paraeid="{f5f764c7-e903-4c0d-8a9e-fcdaf00beb7b}{22}" paraid="1494031890">VNR: <a href="https://videos.cern.ch/record/2295778">https://videos.cern.ch/record/2295778</a></p> <p paraeid="{f5f764c7-e903-4c0d-8a9e-fcdaf00beb7b}{22}" paraid="1494031890">The LS2 upgrades to the LHC detectors: <a href="https://videos.cern.ch/record/2295775" rel="noreferrer" target="_blank">https://videos.cern.ch/record/2295775</a></p> <p paraeid="{f5f764c7-e903-4c0d-8a9e-fcdaf00beb7b}{33}" paraid="1729970185">The LS2 upgrades to the CERN accelerators chain: <a href="https://videos.cern.ch/record/2295776" rel="noreferrer" target="_blank">https://videos.cern.ch/record/2295776</a></p> <p paraeid="{f5f764c7-e903-4c0d-8a9e-fcdaf00beb7b}{33}" paraid="1729970185">The LHC and the accelerator complex: <a href="https://home.cern/resources?title=&amp;topic=1114&amp;type=61&amp;audience=22&amp;field_p_resource_display_tags_target_id=&amp;date_from=&amp;date_to=" rel="noreferrer" target="_blank">here</a></p> <p lang="EN-US" paraeid="{d579d6c3-4292-4a16-9b84-8bef6a23d1d1}{17}" paraid="1860132073" xml:lang="EN-US" xml:lang="EN-US"><strong>Photos:</strong></p> <p lang="EN-US" paraeid="{d579d6c3-4292-4a16-9b84-8bef6a23d1d1}{17}" paraid="1860132073" xml:lang="EN-US" xml:lang="EN-US">Photos of the restart: <a href="https://cds.cern.ch/record/2807018">https://cds.cern.ch/record/2807018</a> </p> <p lang="EN-US" paraeid="{d579d6c3-4292-4a16-9b84-8bef6a23d1d1}{138}" paraid="180576090" xml:lang="EN-US" xml:lang="EN-US">The accelerator complex: <a href="https://home.cern/resources/image/accelerators/accelerator-complex-images-gallery" rel="noreferrer" target="_blank">https://home.cern/resources/image/accelerators/accelerator-complex-images-gallery</a></p> <p lang="EN-US" paraeid="{b60bf66c-0a04-4c6c-91af-c07a2cc71887}{5}" paraid="1121337103" xml:lang="EN-US" xml:lang="EN-US">The LHC: <a href="https://home.cern/resources/image/accelerators/lhc-images-gallery" rel="noreferrer" target="_blank">https://home.cern/resources/image/accelerators/lhc-images-gallery</a></p> <p><strong>Media kit: </strong></p> <p><a href="https://home.cern/press/2022">https://home.cern/press/2022</a></p> </div> <span><span lang="" about="/user/33340" typeof="schema:Person" property="schema:name" datatype="">ochriste</span></span> <span>Wed, 04/20/2022 - 14:29</span> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-04-22T10:16:00Z">Fri, 04/22/2022 - 12:16</time> </div> </div> Wed, 20 Apr 2022 12:29:07 +0000 ochriste 181997 at https://home.web.cern.ch CMS measures the mass of the top quark with unparalleled accuracy https://home.web.cern.ch/news/news/physics/cms-measures-mass-top-quark-unparalleled-accuracy <span>CMS measures the mass of the top quark with unparalleled accuracy</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p class="Body" style="border:medium none; margin-bottom:16px">The CMS collaboration at the <a href="https://home.cern/science/accelerators/large-hadron-collider">Large Hadron Collider</a> (LHC) has performed the most accurate ever measurement of the mass of the top quark – the heaviest known elementary particle. The latest CMS <a href="http://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/TOP-20-008/index.html">result</a> estimates the value of the top-quark mass with an accuracy of about 0.22%. The substantial gain in accuracy comes from new analysis methods and improved procedures to consistently and simultaneously treat different uncertainties in the measurement.</p> <p>The precise knowledge of the top-quark mass is of paramount importance to understand our world at the smallest scale. Knowing this heaviest elementary particle as intimately as possible is crucial because it allows testing of the internal consistency of the mathematical description of all elementary particles, called the <a href="https://home.cern/science/physics/standard-model">Standard Model</a>.</p> <p>For example, if the masses of the <a href="https://home.cern/science/physics/w-boson-sunshine-and-stardust">W boson</a> and <a href="https://home.cern/science/physics/higgs-boson">Higgs boson</a> are known accurately, the top-quark mass can be predicted by the Standard Model. Likewise, using the top-quark and Higgs-boson masses, the W-boson mass can be predicted. Interestingly, despite much progress, the theoretical-physics definition of mass, which has to do with the effect of quantum-physics corrections, is still tough to pin down for the top quark.</p> <p>And remarkably, our knowledge of the very stability of our universe depends on our combined knowledge of the Higgs-boson and top-quark masses. We only know that the universe is very close to a metastable state with the precision of the current measurements of the top-quark mass. If the top-quark mass was even slightly different, the universe would be less stable in the long term, potentially eventually disappearing in a violent event similar to the Big Bang.</p> <p>To make their latest measurement of the top-quark mass, using data from proton–proton LHC collisions collected by the CMS detector in 2016, the CMS team measured five different properties of collision events in which a pair of top quarks is produced, instead of the up to three properties that were measured in previous analyses. These properties depend on the top-quark mass.</p> <p>Furthermore, the team performed an extremely precise calibration of the CMS data and gained an in-depth understanding of the remaining experimental and theoretical uncertainties and their interdependencies. With this innovative method, all of these uncertainties were also extracted during the mathematical fit that determines the final value of the top-quark mass, and this meant that some of the uncertainties could be estimated much more accurately. The result, 171.77<span dir="RTL" lang="AR-SA" style="font-family:&quot;Arial Unicode MS&quot;,sans-serif" xml:lang="AR-SA">±</span>0.38 GeV, is consistent with the previous measurements and the prediction from the Standard Model.</p> <p>The CMS collaboration has made a significant leap forward with this new method to measure the top-quark mass. The cutting-edge statistical treatment of uncertainties and the use of more properties have vastly improved the measurement. Another big step is expected when the new approach is applied to the more extensive dataset recorded by the CMS detector in 2017 and 2018.</p> <p>_____</p> <p><em>Read more on the <a href="https://cms.cern/news/cms-collaboration-measures-mass-top-quark-unparalleled-accuracy">CMS website</a>.</em></p> </div> <span><span lang="" about="/user/159" typeof="schema:Person" property="schema:name" datatype="">abelchio</span></span> <span>Tue, 04/19/2022 - 10:12</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/cms-collaboration" hreflang="en">CMS collaboration</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-04-19T07:38:45Z">Tue, 04/19/2022 - 09:38</time> </div> </div> Tue, 19 Apr 2022 08:12:04 +0000 abelchio 181951 at https://home.web.cern.ch Brazil to become an Associate Member State of CERN https://home.web.cern.ch/news/press-release/cern/brazil-become-associate-member-state-cern <span>Brazil to become an Associate Member State of CERN</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p><span style="font-size:12pt"><span style="font-family:&quot;Calibri&quot;,sans-serif"><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB">On 3 March 2022, CERN Director-General Fabiola Gianotti and Brazilian Minister for Science, Technology and Innovation Marcos Pontes signed an agreement admitting Brazil as an Associate Member State of CERN<sup>1</sup>. The Associate Membership will enter into force once Brazil has completed all necessary accession and ratification processes. Brazil will be the first country in Latin America to join CERN as an Associate Member State. </span></span></span></p> <p><span style="font-size:12pt"><span style="font-family:&quot;Calibri&quot;,sans-serif"><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB">“We are very pleased to welcome Brazil as an Associate Member State. Over the past three decades, Brazilian scientists have contributed substantially to many CERN projects. This agreement enables Brazil and CERN to further strengthen our collaboration, opening up a broad range of new and mutually beneficial opportunities in fundamental research, technological developments and innovation, and education and training activities,” </span><span lang="EN-US" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-US">said Fabiola Gianotti, </span><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB">CERN Director-General</span><span lang="EN-US" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-US">.</span></span></span></p> <p><span style="font-size:12pt"><span style="font-family:&quot;Calibri&quot;,sans-serif"><span lang="EN-US" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-US"><span style="color:black">“The accession of Brazil to CERN Associate Membership creates a robust framework for collaboration in research, technology development and innovation. The Brazilian scientific community has collaborated with CERN since its creation. Being an Associate Member State will foster novel opportunities for our scientists and engineers to participate in activities developed at CERN. Our industry will benefit as well through the participation in contract bids for both R&amp;D and </span></span><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB"><span style="color:black">the </span></span><span lang="EN-US" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-US"><span style="color:black">supply of services and materials. I am certain</span></span><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB"><span style="color:black"> that</span></span><span lang="EN-US" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-US"><span style="color:black"> this partnership will take the Brazilian </span></span><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB"><span style="color:black">science, technology and innovation sector</span></span> <span lang="EN-US" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-US"><span style="color:black">to a whole new level of development</span></span><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB"><span style="color:black">,</span></span><span lang="EN-US" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-US"><span style="color:black">” said </span></span><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB">Marcos Pontes, Brazilian Minister for Science, Technology and Innovation</span><sup>1</sup><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB">.</span></span></span></p> <p><span style="font-size:12pt"><span style="font-family:&quot;Calibri&quot;,sans-serif"><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB">Formal cooperation between CERN and Brazil started in 1990 with the signature of an International Cooperation Agreement, allowing Brazilian researchers to participate in the DELPHI experiment at the Large Electron–Positron Collider (LEP). Today, Brazilian institutes participate in all the main experiments at the Large Hadron Collider (LHC): ALICE, ATLAS, CMS and LHCb. They are also involved in several other experiments and R&amp;D programmes, such as ALPHA, ProtoDUNE at the Neutrino Platform, ISOLDE, Medipix and RD51. Brazilian nationals also participate very actively in CERN training and outreach programmes, including the Summer Student programme, the Portuguese-Language Teacher programme and the Beamline for Schools competition.</span></span></span></p> <p><span style="font-size:12pt"><span style="font-family:&quot;Calibri&quot;,sans-serif"><span lang="EN-GB" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-GB">Over the past decade, Brazil’s experimental particle-physics community has doubled in size. At the four main LHC experiments alone, more than 180 Brazilian scientists, engineers and students collaborate in fields ranging from hardware and data processing to physics analysis. Beyond particle physics, CERN and Brazil’s National Centre for Research in Energy and Materials (CNPEM) have also been formally cooperating since December 2020 on accelerator technology R&amp;D and its applications.</span></span></span></p> <p><span style="font-size:12pt"><span style="font-family:&quot;Calibri&quot;,sans-serif"><span lang="EN-US" style="font-family:&quot;Arial&quot;,sans-serif" xml:lang="EN-US">As an Associate Member State, Brazil will attend meetings of the CERN Council and the Finance Committee. Brazilian nationals will be eligible for limited-duration staff positions, fellowships and studentships. Brazilian companies will be able to bid for CERN contracts, increasing opportunities for industrial collaboration in advanced technologies.</span></span></span></p> <div> <hr align="left" size="1" width="33%" /><div id="ftn1"> <p><span style="font-size:12pt"><span style="font-family:&quot;Calibri&quot;,sans-serif"><sup>1</sup><span lang="EN-US" style="font-size:10.0pt" xml:lang="EN-US"><span style="font-family:&quot;Arial&quot;,sans-serif">Marcos Pontes served as Brazilian Minister for Science, Technology and Innovation until 31 March 2022.</span></span></span></span></p> </div></div></div> <span><span lang="" about="/user/139" typeof="schema:Person" property="schema:name" datatype="">ssanchis</span></span> <span>Tue, 04/12/2022 - 08:58</span> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-04-12T13:00:00Z">Tue, 04/12/2022 - 15:00</time> </div> </div> Tue, 12 Apr 2022 06:58:27 +0000 ssanchis 181904 at https://home.web.cern.ch LHCb reveals secret of antimatter creation in cosmic collisions https://home.web.cern.ch/news/news/physics/lhcb-reveals-secret-antimatter-creation-cosmic-collisions <span>LHCb reveals secret of antimatter creation in cosmic collisions</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>At the <a href="https://indico.cern.ch/event/895086/">Quark Matter conference</a> today and at the recent <a href="https://moriond.in2p3.fr/2022/QCD/">Rencontres de Moriond</a> conference, the LHCb collaboration presented an <a href="https://lhcb-outreach.web.cern.ch/2022/04/07/lhcb-measurements-help-to-understand-possible-signatures-of-dark-matter-presence-in-the-universe/">analysis</a> of particle collisions at the <a href="/science/accelerators/large-hadron-collider">Large Hadron Collider</a> (LHC) that may help determine whether or not any antimatter seen by experiments in space originates from the <a href="/science/physics/dark-matter">dark matter</a> that holds galaxies such as the Milky Way together.</p> <p>Space-based experiments such as the <a href="/science/experiments/ams">Alpha Magnetic Spectrometer </a>(AMS), which was assembled at CERN and is installed on the International Space Station, have detected the fraction of antiprotons, the <a href="/science/physics/antimatter">antimatter</a> counterparts of protons, in high-energy particles called <a href="/science/physics/cosmic-rays-particles-outer-space">cosmic rays</a>. These antiprotons could be created when dark-matter particles collide with each other, but they could also be formed in other instances, such as when protons collide with atomic nuclei in the interstellar medium, which is mainly made up of hydrogen and helium.</p> <p>To find out whether or not any of these antiprotons originate from dark matter, physicists therefore have to estimate how often antiprotons are produced in collisions between protons and hydrogen as well as between protons and helium. While some measurements of the first have been made, and LHCb <a href="https://lhcb-outreach.web.cern.ch/2017/03/27/measurement-of-antiproton-production-in-p-he-collisions/">reported in 2017</a> the first-ever measurement of the second, that LHCb measurement involved only prompt antiproton production – that is, antiprotons produced right at the place where the collisions took place.</p> <p>In their new study, the LHCb team looked also for antiprotons produced at some distance from the collision point, through the transformation, or “decay”, of particles called antihyperons into antiprotons. To make this new measurement and the previous one, the LHCb researchers, who usually use data from proton–proton collisions for their investigations, used instead data from proton–helium collisions obtained by injecting helium gas into the point where the two LHC proton beams would normally collide.</p> <p>By analysing a sample of some 34 million proton–helium collisions and measuring the ratio of the production rate of antiprotons from antihyperon decays to that of prompt antiprotons, the LHCb researchers found that, at the collision energy scale of their measurement, the antiprotons produced via antihyperon decays contribute much more to the total antiproton production rate than the amount predicted by most models of antiproton production in proton–nucleus collisions.</p> <p>“This result complements our previous measurement of prompt antiproton production, and it will improve the predictions of the models,” says LHCb spokesperson Chris Parkes. “This improvement may in turn help space-based experiments find evidence of dark matter.”</p> <p>“Our technique of injecting gas into the LHCb collision point was originally conceived to measure the size of the proton beams,” says LHCb physics coordinator Niels Tuning. “It is really nice to see again that it also improves our knowledge of how often antimatter should be created in cosmic collisions between protons and atomic nuclei.”</p> <p><strong>Additional information</strong></p> <p>Video: </p> <p><a href="https://videos.cern.ch/record/2295741">https://videos.cern.ch/record/2295741</a></p> <p>Pictures:</p> <p><a href="https://cds.cern.ch/record/2639202/files/201809-232_03.jpg?subformat=icon-1440">https://cds.cern.ch/record/2639202/files/201809-232_03.jpg?subformat=icon-1440</a></p> <p><a href="https://cds.cern.ch/record/2302374/files/201802-025_08.jpg?subformat=icon-1440">https://cds.cern.ch/record/2302374/files/201802-025_08.jpg?subformat=icon-1440</a></p> <p> </p> </div> <span><span lang="" about="/user/18835" typeof="schema:Person" property="schema:name" datatype="">mailys</span></span> <span>Wed, 04/06/2022 - 15:02</span> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-04-07T14:00:00Z">Thu, 04/07/2022 - 16:00</time> </div> </div> Wed, 06 Apr 2022 13:02:04 +0000 mailys 181848 at https://home.web.cern.ch ATLAS strengthens its search for supersymmetry https://home.web.cern.ch/news/news/physics/atlas-strengthens-its-search-supersymmetry <span>ATLAS strengthens its search for supersymmetry</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>Where is all the new physics? In the decade since the <a href="http://home.cern/science/physics/higgs-boson">Higgs boson</a>’s discovery, there have been no statistically significant hints of new particles in data from the <a href="https://home.cern/science/accelerators/large-hadron-collider">Large Hadron Collider</a> (LHC). Could they be sneaking past the standard searches? At the recent <a href="https://moriond.in2p3.fr/2022/">Rencontres de Moriond conference</a>, the ATLAS collaboration at the LHC presented several results of novel types of searches for particles predicted by supersymmetry.</p> <p>Supersymmetry, or SUSY for short, is a promising theory that gives each elementary particle a “superpartner”, thus solving several problems in the current <a href="https://home.cern/science/physics/standard-model">Standard Model</a> of particle physics and even providing a possible candidate for <a href="https://home.cern/science/physics/dark-matter">dark matter</a>. ATLAS’s new searches targeted charginos and neutralinos – the heavy superpartners of force-carrying particles in the Standard Model – and sleptons – the superpartners of Standard Model matter particles called leptons. If produced at the LHC, these particles would each transform, or “decay”, into Standard Model particles and the lightest neutralino, which does not further decay and is taken to be the dark-matter candidate.</p> <p>ATLAS’s <a href="https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2022-006/">newest search</a> for charginos and sleptons studied a particle-mass region <a href="https://atlas.cern/updates/briefing/strong-constraints-supersymmetric-dark-matter">previously unexplored</a> due to a challenging background of Standard Model processes that mimics the signals from the sought-after particles. The ATLAS researchers designed dedicated searches for each of these SUSY particle types, using all the data recorded from Run 2 of the LHC and looking at the particles’ decays into two charged leptons (electrons or muons) and “missing energy” attributed to neutralinos. They used new methods to extract the putative signals from the background, including machine-learning techniques and “data-driven” approaches.</p> <p>These searches revealed no significant excess above the Standard Model background. They allowed the ATLAS teams to exclude SUSY particle masses, including slepton masses up to 180 GeV. This slepton mass limit <a href="https://lepsusy.web.cern.ch/lepsusy/">surpasses limits</a> at low mass that were set by experiments at the LHC’s predecessor – the <a href="https://home.cern/science/accelerators/large-electron-positron-collider">Large Electron–Positron</a> (LEP) collider – and that have stood for nearly twenty years. Moreover, it rules out some of the scenarios that could explain the long-standing anomaly associated with the magnetic moment of the muon, which has recently been <a href="https://news.fnal.gov/2021/04/first-results-from-fermilabs-muon-g-2-experiment-strengthen-evidence-of-new-physics/">corroborated by the Muon g-2 experiment</a> at Fermilab in the US.</p> <p>ATLAS physicists have also released the results of a new search for chargino–neutralino pairs, following up on some <a href="https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/SUSY-2017-03/">previous small excesses</a> seen in early analyses of Run 2 data. They studied collision events where the chargino and neutralino decay via <a href="https://home.cern/science/physics/w-boson-sunshine-and-stardust">W</a> and <a href="https://home.cern/science/physics/z-boson">Z</a> bosons respectively, with the W boson decaying to “jets” of particles and the Z boson to a pair of leptons. When the mass difference between the produced neutralino and the lightest possible neutralino lies below the Z boson mass, it is harder to select the signal events and the backgrounds are more challenging to model. This is the first ATLAS result in this decay channel to target this difficult mass region. The search found no significant deviation from the Standard Model prediction and led to new bounds on SUSY particle masses.</p> <p>With the LHC set to begin its third data-taking run, ATLAS physicists are looking forward to building on these exciting results to continue their SUSY searches, in particular by targeting SUSY models that are well motivated theoretically and offer solutions to existing tensions between measurements and Standard Model predictions.</p> <p>_____</p> <p><em>Read more on the <a href="https://atlas.cern/updates/briefing/strengthening-SUSY-searches">ATLAS</a> website.</em></p> </div> <span><span lang="" about="/user/159" typeof="schema:Person" property="schema:name" datatype="">abelchio</span></span> <span>Mon, 04/04/2022 - 17:40</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/atlas-collaboration" hreflang="en">ATLAS collaboration</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-04-06T08:30:00Z">Wed, 04/06/2022 - 10:30</time> </div> </div> Mon, 04 Apr 2022 15:40:11 +0000 abelchio 181831 at https://home.web.cern.ch MoEDAL gets a new detector https://home.web.cern.ch/news/news/physics/moedal-gets-new-detector <span>MoEDAL gets a new detector</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>The MoEDAL collaboration at the <a href="https://home.cern/science/accelerators/large-hadron-collider">Large Hadron Collider</a> (LHC) is adding a new detector to its experiment, in time for the start of the next run of the collider this coming summer. Named as the MoEDAL Apparatus for Penetrating Particles, or MAPP for short, the new detector will expand the physics scope of <a href="https://home.cern/science/experiments/moedal-mapp">MoEDAL</a> to include searches for minicharged particles and long-lived particles.</p> <p>MoEDAL’s current portfolio of searches for new unknown particles includes searches for magnetic monopoles, theoretical particles with a magnetic charge, and dyons, theoretical particles with both magnetic and electric charge. These searches are conducted using two detector systems, one consisting of detectors that track particles and measure their charge, and another comprising detectors that trap particles for further investigation.</p> <p>Using these tracking and trapping detector systems, the MoEDAL team has chalked up several achievements, including narrowing the regions of where to look for <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.021802">point-like magnetic monopoles</a>, the first search at a particle accelerator for <a href="https://home.cern/news/news/physics/moedal-hunts-dyons">dyons</a>, and more recently the first search at a particle collider for <a href="https://home.cern/news/news/physics/moedal-bags-first">Schwinger monopoles</a>, which have a finite size.</p> <p>The new MAPP detector, which is currently being installed in a tunnel adjacent to the LHC tunnel, consists of two main parts. One part, MAPP-mCP, will search for minicharged particles (mCP) – particles with a fractional charge as small as a thousandth of the electron’s charge – using scintillation bars. Another part of the detector, MAPP-LLP, will search for long-lived particles (LLP) employing so-called scintillator hodoscopes arranged in a ‘Russian doll’ configuration.</p> <p>“MoEDAL-MAPP will allow us to explore many models of physics phenomena beyond the <a href="https://home.cern/science/physics/standard-model">Standard Model</a> of particle physics, in ways that are complementary to those of the other LHC detectors,” says MoEDAL spokesperson Jim Pinfold.</p> </div> <span><span lang="" about="/user/159" typeof="schema:Person" property="schema:name" datatype="">abelchio</span></span> <span>Mon, 03/28/2022 - 14:40</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/ana-lopes" hreflang="en">Ana Lopes</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-03-28T12:40:00Z">Mon, 03/28/2022 - 14:40</time> </div> </div> Mon, 28 Mar 2022 12:40:59 +0000 abelchio 181699 at https://home.web.cern.ch CERN Council takes further measures in response to the invasion of Ukraine https://home.web.cern.ch/news/news/cern/cern-council-takes-further-measures-response-invasion-ukraine <span>CERN Council takes further measures in response to the invasion of Ukraine</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>In response to the military invasion of Ukraine by the Russian Federation, the 23 Member States of CERN today decided to:</p> <ul> <li>suspend the participation of CERN scientists in all scientific committees of institutions located in the Russian Federation and the Republic of Belarus, and vice versa; </li> <li>suspend or, failing that, cancel all events jointly arranged between CERN and institutions located in the Russian Federation and the Republic of Belarus;</li> <li>suspend the granting of contracts of association as associated members of the CERN personnel to any new individuals affiliated to home institutions in Russia and Belarus.</li> </ul> <p>Regarding relations with the Joint Institute for Nuclear Research (JINR), with which CERN holds reciprocal Observer status, the CERN Council decided:</p> <ul> <li>to suspend the participation of CERN scientists in all JINR scientific committees, and vice versa;</li> <li>to suspend or, failing that, cancel all events jointly arranged between CERN and JINR;</li> <li>that CERN will not engage in new collaborations with JINR until further notice;</li> <li>that the Observer status of JINR at the Council is suspended and CERN will not exercise the rights resulting from its Observer status at JINR, until further notice.</li> </ul> <p>The CERN Council also decided that, with a view to making a decision at its Session in June 2022 on the suspension of the international cooperation agreements and the related protocols and addenda, as well as any other agreements, including <em>mutatis mutandis</em> experiment memoranda of understanding, allowing for the participation of the Russian Federation and the Republic of Belarus, their national institutes and JINR in the CERN scientific programme, the Council will consider additional information and an action plan, and will further analyse the full consequences of such a decision.</p> <p>The 23 Member States of CERN reiterate their condemnation, in the strongest terms, of the military invasion of Ukraine by the Russian Federation and strongly condemn the statements by those Russian institutes that have expressed support for the illegal invasion of Ukraine.</p> <p>The CERN Council emphasised that the unprovoked and premeditated attack on Ukraine has caused widespread loss of life and a humanitarian crisis. Therefore, the Council stressed that its decisions are taken to express its solidarity with the Ukrainian people and its commitment to science for peace.</p> <p>The core values of the Organization have always been premised upon scientific collaboration across borders as a driver for peace. Therefore, the aggression of one country by another runs against the values for which the Organization stands.</p> <p>The measures agreed on today complement those adopted at the CERN Council’s <a href="/news/news/cern/cern-council-responds-russian-invasion-ukraine">Extraordinary Session</a> held on 8 March, whereby it supported initiatives in favour of the Ukrainian scientific community, condemned the military invasion of Ukraine by the Russian Federation with the involvement of Belarus, suspended the Observer status of the Russian Federation until further notice, and decided that CERN would not engage in new collaborations with the Russian Federation and its institutions until further notice.</p> </div> <span><span lang="" about="/user/18835" typeof="schema:Person" property="schema:name" datatype="">mailys</span></span> <span>Fri, 03/25/2022 - 14:33</span> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-03-25T17:35:00Z">Fri, 03/25/2022 - 18:35</time> </div> </div> Fri, 25 Mar 2022 13:33:38 +0000 mailys 181552 at https://home.web.cern.ch Mass matters when quarks cross a quark–gluon plasma https://home.web.cern.ch/news/news/physics/mass-matters-when-quarks-cross-quark-gluon-plasma <span>Mass matters when quarks cross a quark–gluon plasma</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>Unlike electrons, quarks cannot wander freely in ordinary matter. They are confined by the strong force within hadrons such as the protons and neutrons that make up atomic nuclei. However, at very high energy densities, such as those that are achieved in collisions between nuclei at the <a href="https://home.cern/science/accelerators/large-hadron-collider">Large Hadron Collider</a> (LHC), a different phase of matter exists in which quarks and the mediators of the strong force, gluons, are not confined within hadrons. This form of matter, called a quark–gluon plasma, is thought to have filled the universe in the first few millionths of a second after the Big Bang, before atomic nuclei formed.</p> <p>At the <a href="https://moriond.in2p3.fr/2022/">Rencontres de Moriond conference</a> today, the ALICE collaboration at the LHC reported an <a href="https://arxiv.org/abs/2202.00815">analysis</a> of head-on collisions between lead nuclei showing that quark mass matters when quarks cross a quark–gluon plasma.</p> <p>Hadrons containing charm and beauty quarks, the heavier cousins of the up and down quarks that make up protons and neutrons, offer an excellent way to study the properties of the quark–gluon plasma, such as its density. A charm quark is much heavier than a proton, and a beauty quark is as heavy as five protons. These quarks are produced in the very first instants of the collisions between nuclei, before the formation of the quark–gluon plasma that they then traverse. Therefore, they interact with the plasma’s constituents throughout its entire evolution.</p> <p>Just like electrically charged particles crossing an ordinary gas can tell us about its density, through the energy they lose in the crossing, heavy quarks can be used to determine the density of the quark–gluon plasma through the energy they lose in strong interactions with the plasma’s constituents. However, before using the energy loss in the plasma to measure the plasma’s density, physicists need to validate the theoretical description of this loss.</p> <p>A fundamental prediction of the theory of the strong force is that quarks that have a larger mass lose less energy than their lighter counterparts because of a mechanism known as the dead-cone effect, which prevents the radiation of gluons and thus of energy in a cone around the quark’s direction of flight.</p> <p>In their new <a href="https://arxiv.org/abs/2202.00815">study</a> of head-on collisions between lead nuclei, the ALICE collaboration tested this prediction using measurements of charm-quark-containing particles called D mesons. They measured D mesons produced right after the collisions from initial charm quarks, called ‘prompt’ D mesons, as well as ‘non-prompt’ D mesons produced later in the decays of B mesons, which contain the heavier beauty quarks. They presented the measurements in terms of the nuclear modification factor, which is a scaled ratio of particle production in lead–lead collisions to that in proton–proton collisions (figure below). They found that the production of non-prompt D mesons (blue markers in the figure) in lead–lead collisions is less suppressed than that of prompt D mesons (red markers).</p> <figure class="cds-image align-right" id="CERN-HOMEWEB-PHO-2022-048-1"><a href="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-048-1" title="View on CDS"><img alt="home.cern,Experiments and Tracks" src="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-048-1/file?size=large" /></a> <figcaption>Comparison of the nuclear modification factor of D mesons produced from initial charm quarks (red) and from the decays of hadrons containing beauty quarks (blue), as a function of the particles’ transverse momentum. Particle-production suppression (deviation from unity) is attributed to quark interactions in the quark–gluon plasma. <span> (Image: CERN)</span></figcaption></figure> <p>These results are described well by models in which beauty quarks lose less energy than charm quarks in the quark–gluon plasma, because of their larger mass. They thus confirm the theoretical expectations of the role of quark mass in the interactions of quarks with the quark–gluon plasma. In addition, the measurements are sensitive to B mesons that have low energies. This is crucial when it comes to using beauty quarks to determine the density and other properties of the plasma.</p> <p>Further measurements with the <a href="https://home.cern/news/news/experiments/upgrading-alice-whats-store-next-two-years">upgraded ALICE detector</a> in the next run of the LHC, which is scheduled to start this coming summer, will help to better understand the theoretical description of the energy loss that quarks experience when they cross the quark–gluon plasma.</p> <p>_____</p> <p><em>Read more on the <a href="https://alice-collaboration.web.cern.ch/node/35282">ALICE</a> website.</em></p> </div> <span><span lang="" about="/user/159" typeof="schema:Person" property="schema:name" datatype="">abelchio</span></span> <span>Wed, 03/23/2022 - 16:37</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/alice-collaboration" hreflang="en">ALICE collaboration</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-03-25T08:50:00Z">Fri, 03/25/2022 - 09:50</time> </div> </div> Wed, 23 Mar 2022 15:37:21 +0000 abelchio 181365 at https://home.web.cern.ch ATLAS nets top quark produced together with a photon https://home.web.cern.ch/news/news/physics/atlas-nets-top-quark-produced-together-photon <span>ATLAS nets top quark produced together with a photon</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>The top quark is very special. It’s the heaviest known elementary particle and therefore strongly interacts with the <a href="https://home.cern/science/physics/higgs-boson">Higgs boson</a>. The top quark’s interactions with other particles provide promising leads for searches for physics beyond the <a href="https://home.cern/science/physics/standard-model">Standard Model</a>. By taking accurate measurements of its properties using rare processes, physicists can explore new physics phenomena at the highest energies.</p> <p>At the ongoing <a href="https://moriond.in2p3.fr/2022/">Rencontres de Moriond conference</a>, the ATLAS collaboration at the <a href="https://home.cern/science/accelerators/large-hadron-collider">Large Hadron Collider</a> (LHC) <a href="https://moriond.in2p3.fr/2022/EW/slides/2/1/3_MAlhroob.pdf">announced</a> the <a href="https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2022-013/">observation</a> of one of these rare processes: the production of a single top quark in association with a photon through the electroweak interaction. With a statistical significance well above five standard deviations, the result represents the first observation of top-quark–photon production. This achievement was far from straightforward, as the search for this process was dominated by a large number of background collision events that mimic top-quark–photon production.</p> <p>In their new analysis, the ATLAS researchers analysed the full LHC Run 2 data set, recorded by the detector between 2015 and 2018. They focused on collision events where the top quark decays via a W boson to an electron or a muon and a neutrino, and to a bottom quark. They further narrowed their search by seeking out a particular characteristic of top-quark–photon events: a “forward jet”, which is a spray of particles that is commonly produced and travels at small angles to the LHC’s proton beams.</p> <p>To separate the top-quark–photon events from the background events, the ATLAS researchers used a neural network, which receives as input a number of variables or features, and finds the combination of those features that most accurately classifies a data event according to signal or background types.</p> <p>The statistical significance of the ATLAS measurement of top-quark–photon production is 9.1 standard deviations – well above the 5 standard-deviation threshold required to claim observation of a process in particle physics. The expected significance, based on the Standard Model prediction, was 6.7 standard deviations.</p> <p>This exciting measurement will allow physicists to look for hints of new interactions that might exist beyond the reach of the LHC. In particular, physicists can now use this process to infer information on new particles that could alter the top-quark–photon interaction. Further studies with new analysis techniques and a significantly larger data set from the upcoming Run 3 of the LHC promise an exciting road ahead.</p> <p>_____</p> <p><em>Read more on the <a href="https://atlas.cern/updates/briefing/single-top-photon-observation">ATLAS</a> website.</em></p> </div> <span><span lang="" about="/user/159" typeof="schema:Person" property="schema:name" datatype="">abelchio</span></span> <span>Wed, 03/23/2022 - 16:29</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/atlas-collaboration" hreflang="en">ATLAS collaboration</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-03-24T10:00:00Z">Thu, 03/24/2022 - 11:00</time> </div> </div> Wed, 23 Mar 2022 15:29:49 +0000 abelchio 181364 at https://home.web.cern.ch ATLAS seeks out unusual signatures of long-lived particles https://home.web.cern.ch/news/news/physics/atlas-seeks-out-unusual-signatures-long-lived-particles <span>ATLAS seeks out unusual signatures of long-lived particles</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>High-energy collisions at the Large Hadron Collider (LHC) allow researchers to clearly study heavy Standard Model particles, like the Higgs boson, that decay almost immediately at the LHC collision point. However, new long-lived particles (LLPs) could travel sizeable distances through the ATLAS detector before decaying.</p> <p>Studying the decay of any particle is a complex task, but it is usually made much easier by assuming that it decayed near the LHC collision point. This leaves LLPs in a blind spot, as they could decay anywhere in the detector. To ensure no stone is left unturned, ATLAS physicists have devised a range of new strategies to look for LLPs with various possible characteristics.</p> <p><strong>The hunt for right-handed neutrinos</strong></p> <p>Neutrinos have long puzzled physicists, as they have only ever been observed to be “left-handed” (i.e. their spin and momentum are opposed), while all other particles can also be observed in “right-handed” states. One possibility is that right-handed neutrinos exist but are very heavy, and therefore harder to produce in nature. These particles – called “heavy neutral leptons” (HNLs) – could also explain why neutrinos are so light.</p> <p>In a new search for HNLs, ATLAS physicists looked for leptons originating from a common point a short distance from the collision point. The HNL could have decayed to a mixture of electrons, muons and missing energy. Using the decay products, they reconstructed the possible HNL mass and were able to set limits on masses between 3 and ~15 GeV. They also reported on HNL decays to electron–muon pairs for the very first time!</p> <p><strong>Harnessing the power of machine learning</strong></p> <p>If a new, neutral LLP were to decay to quarks in the outer layers of the calorimeter, it would leave behind sprays of collimated particles called “displaced” jets. These would leave an unusual signature in the detector: the jets would have no associated particle trajectories and would be very narrow compared to their Standard Model counterparts (see event display).</p> <p>ATLAS researchers have exploited the uncommon characteristics of displaced jets to search for pairs of neutral LLPs. They developed novel machine-learning methods to distinguish displaced jets from background interactions. No significant excess of events has been spotted so far.</p> <p>But what if the neutral LLP decays to leptons instead of quarks? “Dark photons” are a type of LLP believed to behave this way, and would leave behind collimated sprays of leptons in the detector, called “lepton-jets”. ATLAS’s newest search for dark photons uses machine-learning techniques that exploit patterns of raw energy deposits in each layer of the detector – a first for the collaboration. Although no excess of events was seen, physicists set stringent new limits on the existence of dark photons and were able to probe dark-photon decays to electrons for the very first time!</p> <p><strong>Following the steps of charged LLPs</strong></p> <p>When searching for new particles, physicists have to look for their decay products – or do they? If a heavy charged LLP exists, it would leave abnormally large energy deposits in the ATLAS tracking detector. This is an exceptional case where physicists could actually detect a new particle directly.</p> <figure class="cds-image align-right" id="CERN-HOMEWEB-PHO-2022-042-1"><a href="https://cds.cern.ch/record/2804516" title="View on CDS"><img alt="ATLAS" src="//cds.cern.ch/record/2804516/files/Picture%201.png?subformat=icon-1440" /></a> <figcaption>Result of the ATLAS search for a heavy charged LLP. The observed data (black) agree with the Standard Model expectation (blue line), except for a small excess of events in a high-energy and high-mass region (above 1000 GeV). (Image: ATLAS collaboration/CERN)</figcaption></figure> <p>However, predicting the Standard Model background processes in this search is very challenging. To tackle the problem, ATLAS physicists employed a sophisticated “data-driven” method using tracks with regular energy deposits for comparison. The observed data agree with the Standard Model expectation, except for a small excess of events in a high-energy and high-mass region (see figure). Although intriguing, the measurements made indicate that none of the candidate events match the heavy new particle hypothesis. New searches in the works, and additional data, could shed more light on it.</p> <p><strong>Into Run 3</strong></p> <p>At the heart of these analyses is one key question: what if new particles are hiding from standard searches? ATLAS researchers have developed novel, creative ways to explore the rich diversity of possible LLP decays. The search continues, with Run 3 of the LHC promising new data and new innovations to further this exciting programme of research. </p> <p> </p> <p>Read the full version of this article <a href="https://atlas.cern/updates/briefing/search-long-lived-particles">here</a>.</p> </div> <span><span lang="" about="/user/147" typeof="schema:Person" property="schema:name" datatype="">cagrigor</span></span> <span>Tue, 03/22/2022 - 11:38</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/atlas-collaboration" hreflang="en">ATLAS collaboration</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-03-22T10:26:59Z">Tue, 03/22/2022 - 11:26</time> </div> </div> Tue, 22 Mar 2022 10:38:10 +0000 cagrigor 181357 at https://home.web.cern.ch Largest matter-antimatter asymmetry observed https://home.web.cern.ch/news/news/physics/largest-matter-antimatter-asymmetry-observed <span>Largest matter-antimatter asymmetry observed</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>CP asymmetry is the only non-trivial difference between matter and antimatter found so far. Its discovery in neutral kaon decays in 1964 came as a big surprise to the physics community, but today it is an essential component of the Standard Model of particle physics. Without CP asymmetry the Big Bang would have created equal amounts of matter and antimatter, which would all have then annihilated, leaving behind an empty Universe filled with radiation. To produce a matter-dominated Universe like the one we live in, an excess of matter must have formed and survived this annihilation. But to produce such an excess, some difference between matter and antimatter must be present: enter CP asymmetry. Unfortunately, the amount of CP asymmetry present in the Standard Model of particle physics is not enough to explain the observed composition of the Universe, driving extensive studies of this phenomenon and searches for other sources of CP asymmetry.</p> <p>This week, at the <em>Rencontres de Moriond</em> <em>Electroweak</em> conference and during a <a href="https://indico.cern.ch/event/1137298/">seminar held at CERN</a>, the LHCb collaboration presented new results from studies of CP asymmetry in charmless three-body decays of charged B mesons. These decays involve a charged B meson, consisting of a beauty quark and an up quark, transforming into a combination of π and K mesons. The name “charmless” refers to the absence of charm quarks in the final state: π<sup>±</sup> mesons (pions) contain only up and down quarks, and K<sup>±</sup> mesons (kaons) contain a strange and an up quark. Charmless decays involve the transformation of a beauty quark into an up quark, which is an unlikely process, as the beauty quark predominantly decays into a charm quark. In this rare process the effects of CP violation are expected to be enhanced.</p> <p>The new LHCb results focus on “direct” CP violation: a phenomenon where the same decay process has a different probability for a particle than for an antiparticle. The strongest global asymmetry was observed for the decay into two kaons and one pion, where the probability of a B<sup>+</sup>→π<sup>+</sup>K<sup>+</sup>K<sup>-</sup> decay is about 20% higher than for the B<sup>-</sup>→π<sup>-</sup>K<sup>+</sup>K<sup>-</sup>decay (corresponding to a measured CP asymmetry A<sub>CP</sub> of -0.114). A global CP asymmetry has also been observed with a significance of more than five standard deviations for the first time in decays into three pions and decays into three kaons. For the final state with two pions and one kaon, CP violation is still not confirmed.</p> <p>The three-particle final state can, however, be studied further in order to extract more information. The process of a B meson transforming into three particles can occur in several steps, with intermediate short-lived particles (“resonances”) forming and subsequently decaying into the pions and kaons seen in the final state. These processes can make different contributions to the CP asymmetry and can be disentangled by taking into account the momenta of the final state particles in what’s known as “phase space analysis”. One spectacular result of such an analysis is the indication of a χ<sub>hc</sub><sup>0</sup> meson (containing a charm-anticharm quark pair) being formed during the B→πππ decay. The χ<sub>hc</sub><sup>0</sup> was not expected to contribute to CP violation but the results show the presence of a significant asymmetry. In fact, the subset of data containing the χ<sub>hc</sub><sup>0</sup> events features the highest CP asymmetry ever observed: the B<sup>-</sup> meson makes an almost 7 times greater contribution to this process than its B<sup>+</sup>counterpart, as can be seen in the plot below.</p> <figure class="cds-image" id="CERN-HOMEWEB-PHO-2022-036-1"><a href="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-036-1" title="View on CDS"><img alt="home.cern,Accelerators" src="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-036-1/file?size=large" /></a> <figcaption>Invariant mass of the three pion final state in a pre-defined phase space region. A clear signal from the B- (left plot) and B+ candidates (right plot) is visible as a peak at 5.28 GeV/c2. The difference between the height of these two peaks corresponds to the CP asymmetry in the region under study. <span> (Image: CERN)</span></figcaption></figure> <p>The results presented provide important clues about the mechanism of CP asymmetry generation in the Standard Model, which is not yet fully understood. Even more detailed studies will be performed in the upcoming LHC Run 3 with the newly-upgraded LHCb detector.</p> <p>Read more on the <a href="https://lhcb-outreach.web.cern.ch/">LHCb website</a>.</p> </div> <span><span lang="" about="/user/147" typeof="schema:Person" property="schema:name" datatype="">cagrigor</span></span> <span>Fri, 03/18/2022 - 11:51</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/piotr-traczyk" hreflang="en">Piotr Traczyk</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-03-18T10:32:58Z">Fri, 03/18/2022 - 11:32</time> </div> </div> Fri, 18 Mar 2022 10:51:50 +0000 cagrigor 181322 at https://home.web.cern.ch ASACUSA sees surprising behaviour of hybrid matter–antimatter atoms in superfluid helium https://home.web.cern.ch/news/news/physics/asacusa-sees-surprising-behaviour-hybrid-matter-antimatter-atoms-superfluid <span>ASACUSA sees surprising behaviour of hybrid matter–antimatter atoms in superfluid helium</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>A hybrid matter­­–<a href="/science/physics/antimatter">antimatter</a> helium atom containing an antiproton, the proton’s antimatter equivalent, in place of an electron has an unexpected response to laser light when immersed in superfluid helium, reports the <a href="/science/experiments/asacusa">ASACUSA</a> collaboration at CERN. The result, described in a paper published today in the journal <a href="https://www.nature.com/articles/s41586-022-04440-7"><em>Nature</em></a>, may open doors to several lines of research.</p> <p>“Our study suggests that hybrid matter–antimatter helium atoms could be used beyond particle physics, in particular in condensed-matter physics and perhaps even in astrophysics experiments,” says ASACUSA co-spokesperson Masaki Hori. “We have arguably made the first step in using antiprotons to study condensed matter.”</p> <p>The ASACUSA collaboration is well used to making hybrid matter–antimatter helium atoms to <a href="/news/news/physics/asacusa-improves-measurement-antiproton-mass">determine</a> the antiproton’s mass and compare it with that of the proton. These hybrid atoms contain an antiproton and an electron around the helium nucleus (instead of two electrons around a helium nucleus) and are made by mixing antiprotons produced at CERN’s <a href="/science/accelerators/antiproton-decelerator">antimatter factory</a> with a helium gas that has a low atomic density and is kept at low temperature.</p> <p>Low gas densities and temperatures have played a key role in these antimatter studies, which involve measuring the response of the hybrid atoms to laser light in order to determine their light spectrum. High gas densities and temperatures result in spectral lines, caused by transitions of the antiproton or electron between energy levels, that are too broad, or even obscured, to allow the mass of the antiproton relative to that of the electron to be determined.</p> <p>This is why it came as surprise to the ASACUSA researchers that, when they used liquid helium, which has a much higher density than gaseous helium, in their new study, they saw a decrease in the width of the antiproton spectral lines.</p> <p>Moreover, when they decreased the temperature of the liquid helium to values below the temperature at which the liquid becomes a superfluid, i.e. flows without any resistance, they found an abrupt further narrowing of the spectral lines.</p> <p>“This behaviour was unexpected,” says Anna Sótér, who was the principal PhD student working on the experiment and is now an assistant professor at ETHZ. “The optical response of the hybrid helium atom in superfluid helium is starkly different to that of the same hybrid atom in high-density gaseous helium, as well as that of many normal atoms in liquids or superfluids.”</p> <p>The researchers think that the surprising behaviour observed is linked to the radius of the electronic orbital, i.e. the distance at which the hybrid helium atom’s electron is located. In contrast to that of many normal atoms, the radius of the hybrid atom’s electronic orbital changes very little when laser light is shone on the atom and thus does not affect the spectral lines even when the atom is immersed in superfluid helium. However, further studies are needed to confirm this hypothesis.</p> <p>The result has several ramifications. Firstly, researchers may create other hybrid helium atoms, such as <a href="/news/news/physics/asacusa-researchers-create-and-study-new-exotic-atom-psi">pionic helium atoms</a>, in superfluid helium using different antimatter and exotic particles, to study their response to laser light in detail and measure the particle masses. Secondly, the substantial narrowing of the lines in superfluid helium suggests that hybrid helium atoms could be used to study this form of matter and potentially other condensed-matter phases. Finally, the narrow spectral lines could in principle be used to search for cosmic antiprotons or antideuterons (a nucleus made of an antiproton and an antineutron) of particularly low velocity that hit the liquid or superfluid helium that is used to cool experiments in space or in high-altitude balloons. However, numerous technical challenges must be overcome before the method becomes complementary to existing techniques for searching for these forms of antimatter.</p> <p> </p> <p><strong>Photos</strong></p> <p><a href="https://cds.cern.ch/record/2801207/files/202202-025_50.jpg?subformat=icon-1440">https://cds.cern.ch/record/2801207/files/202202-025_50.jpg?subformat=icon-1440</a></p> <p><a href="https://cds.cern.ch/record/2801207/files/202202-025_15.jpg?subformat=icon-1440">https://cds.cern.ch/record/2801207/files/202202-025_15.jpg?subformat=icon-1440</a></p> <p> </p> <p><strong>Videos</strong></p> <p><a href="https://videos.cern.ch/record/2295468">https://videos.cern.ch/record/2295468</a></p> <p><a href="https://videos.cern.ch/record/2295467">https://videos.cern.ch/record/2295467</a></p> <p> </p> </div> <span><span lang="" about="/user/18835" typeof="schema:Person" property="schema:name" datatype="">mailys</span></span> <span>Thu, 03/03/2022 - 10:43</span> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-03-16T16:00:00Z">Wed, 03/16/2022 - 17:00</time> </div> </div> Thu, 03 Mar 2022 09:43:29 +0000 mailys 178935 at https://home.web.cern.ch Homing in on the Higgs boson's interaction with the charm quark https://home.web.cern.ch/news/news/physics/homing-higgs-bosons-interaction-charm-quark <span>Homing in on the Higgs boson&#039;s interaction with the charm quark</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>Since the discovery of the <a href="https://home.cern/science/physics/higgs-boson">Higgs boson</a> a decade ago, the ATLAS and CMS collaborations at the <a href="https://home.cern/science/accelerators/large-hadron-collider">Large Hadron Collider</a> (LHC) have been hard at work trying to unlock the secrets of this special particle. In particular, they have been investigating in detail how the Higgs boson interacts with fundamental particles such as those that make up matter, that is, quarks and leptons. In the <a href="https://home.cern/science/physics/standard-model">Standard Model</a> of particle physics, these matter particles fall into three categories, or “generations”, of increasing mass, and the Higgs boson interacts with them with a strength that is proportional to their mass. Any deviation from this behaviour would provide a clear indication of new phenomena.</p> <p>ATLAS and CMS have previously observed the interactions of the Higgs boson with the heaviest quarks and leptons, i.e. those of the third generation, which agree with the predictions from the Standard Model within the current measurement precision. They have also <a href="https://home.cern/news/press-release/physics/cern-experiments-announce-first-indications-rare-higgs-boson-process">obtained the first indications</a> that the Higgs boson interacts with a muon, a lepton of the second generation. However, they have yet to observe it interacting with second-generation quarks. In two recent publications, <a href="https://arxiv.org/abs/2201.11428">ATLAS</a> and <a href="http://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/HIG-21-008/index.html">CMS</a> report analyses that place tight limits on the strength of the Higgs boson's interaction with a charm quark, a second-generation quark.</p> <p>ATLAS and CMS study the Higgs boson's interactions by looking at how it transforms, or “decays”, into lighter particles or how it is produced together with other particles. In their latest studies, using data from the second run of the LHC, the two teams searched for the decay of the Higgs boson into a charm quark and its antimatter counterpart, the charm antiquark.</p> <p>In the Standard Model, this decay is relatively rare, occurring only 3% of the time. What’s more, the decay is extremely hard to spot because the two sprays, or “jets”, of particles that it generates can also be produced by other processes at far higher rates. To more easily identify this decay, ATLAS and CMS targeted their searches at Higgs bosons produced together with a <a href="https://home.cern/science/physics/w-boson-sunshine-and-stardust">W</a> or a <a href="https://home.cern/science/physics/z-boson">Z</a> boson decaying to electrons, muons (W, Z) or neutrinos (Z), and they used sophisticated machine-learning techniques to identify jets originating from charm quarks. CMS also looked for high-momentum, or “boosted”, Higgs bosons that result in two charm jets collapsing into a wide jet.</p> <p>The teams found no significant indication of the decay of the Higgs boson into charm quarks in the data, but their analyses set bounds on the rate at which this decay should occur when the Higgs boson is produced along with a W and Z boson. These bounds correspond to upper limits on the interaction strength of the Higgs boson with a charm quark, of 8.5 and 5.5 times the Standard Model prediction in the case of ATLAS and CMS, respectively.</p> <p>The ATLAS team went on to combine their analysis with a <a href="https://atlas.cern/updates/briefing/measuring-beauty-higgs-boson">measurement</a> of the Higgs boson decay into beauty quarks, demonstrating that the Higgs boson interacts more weakly with the charm quark than it does with the beauty quark. In other words, they found that the Higgs boson interacts differently with quarks of the second and third generations, as predicted by the Standard Model.</p> <p>Interestingly, the CMS study allowed the CMS researchers to observe for the first time at a hadron collider the decay of the Z boson into charm quarks, a bonus observation that resulted from a validation step in their search for the decay of the Higgs boson into charm quarks.</p> <p>_____</p> <p><em>Read more on the <a href="https://atlas.cern/updates/briefing/higgs-charm-beauty">ATLAS</a> and <a href="https://cms.cern/news/increased-confidence-higgs-boson-coupling-charm-quark">CMS</a> websites.</em></p> </div> <span><span lang="" about="/user/159" typeof="schema:Person" property="schema:name" datatype="">abelchio</span></span> <span>Thu, 03/10/2022 - 11:52</span> <div class="field field--name-field-p-news-display-byline field--type-entity-reference field--label-above"> <div class="field--label"><b>Byline</b></div> <div class="field--items"> <div class="field--item"><a href="/authors/ana-lopes" hreflang="en">Ana Lopes</a></div> </div> </div> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-03-11T17:00:00Z">Fri, 03/11/2022 - 18:00</time> </div> </div> Thu, 10 Mar 2022 10:52:06 +0000 abelchio 181220 at https://home.web.cern.ch CERN Council responds to Russian invasion of Ukraine https://home.web.cern.ch/news/news/cern/cern-council-responds-russian-invasion-ukraine <span>CERN Council responds to Russian invasion of Ukraine</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>The 23 <a href="/about/who-we-are/our-governance/member-states">Member States</a> of CERN condemn, in the strongest terms, the military invasion of Ukraine by the Russian Federation, and deplore the resulting loss of life and humanitarian impact, as well as the involvement of Belarus in this unlawful use of force against Ukraine.</p> <p>Ukraine is an Associate Member State of CERN, and Ukrainian scientists are active in many of the Laboratory’s experiments and activities. Deeply touched by the widespread and tragic consequences of the aggression, the CERN Management and personnel, as well as the scientific community in CERN’s Member States, are working to contribute to the humanitarian effort in Ukraine and to help the Ukrainian community at CERN.</p> <p>The Council held an Extraordinary Session on 8 March, devoted to discussion of future interactions with Russia. </p> <p>The Council <a href="https://council.web.cern.ch/sites/default/files/c-e-3626_Resolution_re_Russia%20.pdf">decided</a> that:</p> <p>- CERN will promote initiatives to support Ukrainian collaborators and Ukrainian scientific activity in the field of high-energy physics;</p> <p>- the Observer status of the Russian Federation is suspended until further notice;</p> <p>- CERN will not engage in new collaborations with the Russian Federation and its institutions until further notice.  </p> <p>The situation will continue to be monitored carefully and the Council is ready to take any further measures, as appropriate, at its future meetings.</p> <p>In addition, the CERN Management will comply with all applicable international sanctions.</p> <p>The CERN Council also expresses its support to the many members of CERN’s Russian scientific community who reject this invasion.</p> <p>CERN was established in the aftermath of World War II to bring nations and people together for the peaceful pursuit of science: this aggression runs against everything for which the Organization stands.  CERN will continue to uphold its core values of scientific collaboration across borders as a driver for peace.</p> </div> <span><span lang="" about="/user/40" typeof="schema:Person" property="schema:name" datatype="">katebrad</span></span> <span>Tue, 03/08/2022 - 13:18</span> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-03-08T12:52:30Z">Tue, 03/08/2022 - 13:52</time> </div> </div> Tue, 08 Mar 2022 12:18:12 +0000 katebrad 180898 at https://home.web.cern.ch Solidarity with Ukraine https://home.web.cern.ch/news/news/cern/solidarity-ukraine <span>Solidarity with Ukraine</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>CERN was <a href="https://home.cern/about/who-we-are/our-history">established</a> in the aftermath of World War II to bring nations and people together for the peaceful pursuit of science: aggression and war run counter to everything that the Organization stands for. CERN will continue to uphold its core values of scientific collaboration across borders as a driver for peace.</p> <p><strong>Standing with Ukraine</strong></p> <p>Following the invasion and subsequent escalation of aggression by Russian armed forces, a humanitarian crisis has been unfolding in Ukraine, an Associate Member State of CERN. CERN wishes to express solidarity with our Ukrainian colleagues, their families and the entire Ukrainian people. Our thoughts are with everyone whose life has been disrupted by the war.</p> <p>Discussions began among <a href="https://home.cern/about/who-we-are/our-governance">CERN Council</a> delegations concerning the appropriate measures that the Organization should take. As these discussions advanced, an extraordinary meeting of the CERN Council was called by the President of Council on Tuesday 8 March during which a <a href="https://council.web.cern.ch/sites/default/files/c-e-3626_Resolution_re_Russia%20.pdf">Resolution</a> was adopted.</p> <p>The main points of the Council’s Resolution are:</p> <ul> <li>the strong condemnation of Russia's invasion of Ukraine,</li> <li>that Russia’s Observer status to the Council is suspended</li> <li>and that new collaborations with Russian institutes will not be undertaken.</li> </ul> <p>Collaboration between CERN and the Russian scientific community on ongoing projects is maintained, for the time being. CERN will continue to promote initiatives to support Ukrainian scientists and Ukrainian scientific activity in the field of high-energy physics. A summary of the main conclusions was published <a href="https://home.cern/news/news/cern/cern-council-responds-russian-invasion-ukraine">here</a>. </p> <p><strong>Taking action</strong></p> <p>Since the invasion on 24 February, several actions have already been initiated by the Organization to support employed and associated members of personnel of Ukrainian nationality and their families:</p> <ul> <li>CERN's Human Resources department has contacted Ukrainian members of personnel to provide them with material assistance and psychological support. Members of the CERN community can also reach out for help through existing <a href="https://hr.web.cern.ch/Support-Ukraine">support channels</a>.</li> <li>The CERN community is <a href="https://staff-association.web.cern.ch/donations-ukraine">raising funds</a> that will be sent directly to the Office of the International Red Cross in Ukraine. These funds will help meet the immediate needs of the population, including emergency medical care, psychological support, blood donation, and the distribution of food, drink, and other essential items. The CERN Directorate will match, from the CERN budget, donations made by the personnel. The CERN Staff Association will also contribute financially to the collection.</li> </ul> <p>Initiatives of many members of the personnel are also important demonstrations of CERN solidarity and community spirit. The <a href="https://home.cern/solidarity-ukraine">Solidarity with Ukraine webpage</a> will be updated as new initiatives take place.</p> </div> <span><span lang="" about="/user/40" typeof="schema:Person" property="schema:name" datatype="">katebrad</span></span> <span>Mon, 03/07/2022 - 11:47</span> <div class="field field--name-field-p-news-display-pub-date field--type-datetime field--label-above"> <div class="field--label"><b>Publication Date</b></div> <div class="field--item"><time datetime="2022-03-08T12:00:00Z">Tue, 03/08/2022 - 13:00</time> </div> </div> Mon, 07 Mar 2022 10:47:42 +0000 katebrad 180650 at https://home.web.cern.ch