CERN: Physics updates https://home.cern/ en Higgs10: Three-quarters of the way there https://home.cern/news/news/physics/higgs10-three-quarters-way-there <span>Higgs10: Three-quarters of the way there</span> <div class="field field--name-field-p-news-display-body field--type-text-long field--label-hidden field--item"><p>4 July 2012 wasn’t the first time physicists had packed themselves into the CERN auditorium to witness the discovery of a new elementary particle. To rapturous applause on 20 January 1983, Carlo Rubbia, spokesperson of the UA1 experiment at the Spp-barS collider, presented six candidate events for the W boson, the electrically charged carrier of the weak interaction responsible for radioactive decay. In similar scenes the following afternoon, Luigi Di Lella of the UA2 experiment announced four W candidates. Along with the Z boson and massless photon, the W boson is one of three “gauge” bosons of a unified electroweak interaction that demands the existence of a fourth “scalar” particle called the Higgs boson.</p> <p><a href="https://home.cern/news/series/higgs10/higgs-boson-and-rise-standard-model-particle-physics-1970s">Indirect evidence for the Z boson had been obtained a decade earlier at Gargamelle</a>, driving the community to seek a direct discovery of the massive electroweak bosons. But their predicted masses – around 80 and 90 GeV for the W and Z, respectively – were beyond the reach of experiments at the time. In 1976, Rubbia, Peter McIntyre and David Cline suggested modifying the CERN SPS from a one-beam accelerator into a machine that would collide beams of protons and antiprotons, greatly increasing the available energy. <a href="https://cerncourier.com/cws/article/cern/46057">Simon van der Meer</a> had already invented <a href="https://home.cern/about/engineering/stochastic-cooling">a way of producing and storing dense beams</a> of protons or antiprotons, while his “stochastic cooling” method to reduce the energy spread and angular divergence of the beams had been honed at the Intersecting Storage Rings (the world’s first hadron collider). Many doubted the wisdom of the decision, however, especially as CERN was keen to push its visionary Large Electron–Positron (LEP) collider.</p> <figure class="cds-image align-left" id="CERN-HOMEWEB-PHO-2022-102-3"><a href="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-102-3" title="View on CDS"><img alt="home.cern,Personalities and History of CERN" src="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-102-3/file?size=large" /></a> <figcaption>First direct production of the W boson in the UA1 detector in late 1982<span> (Image: CERN)</span></figcaption></figure> <p>As former UA2 spokesperson Pierre Darriulat wrote in <em>CERN Courier</em> in 2004: “The pressure to discover the W and Z was so strong that the long design, development and construction time of the LEP project left most of us, even the most patient, dissatisfied. A quick (but hopefully not dirty) look at the new bosons would have been highly welcome. But when proton–proton colliders such as the Superconducting Intersecting Storage Rings were proposed in this spirit, they were ‘killed in the egg’ by the management at CERN, with the argument that they would delay – or, even worse, endanger – the LEP project. The same argument did not apply to the proton–antiproton collider, as it did not require the construction of a new collider ring and could be proposed as an experiment … Another argument also made it possible for the proton–antiproton project to break the LEP taboo: if CERN did not buy Carlo’s idea, it was most likely that he would sell it to Fermilab.”</p> <p>Two detectors, <a href="https://home.cern/about/experiments/ua1">UA1</a> and <a href="https://home.cern/about/experiments/ua2">UA2</a>, built around the Spp-barS beam pipe to search for signatures of the W and Z particles, started taking collision data in 1981. When they confirmed the existence of the W boson – which was announced at a press conference at CERN on 25 January 1983, followed by the discovery of the Z boson a few months later and the Nobel Prize in Physics for Rubbia and Van der Meer the following year –</p> <figure class="cds-image align-right" id="CERN-HOMEWEB-PHO-2022-102-2"><a href="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-102-2" title="View on CDS"><img alt="home.cern,Personalities and History of CERN" src="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-102-2/file?size=large" /></a> <figcaption><span>First direct production of the Z boson in the UA1 detector in April 1983 (Image: CERN)</span></figcaption></figure> <p> the case for the existence of the Higgs boson grew stronger. That’s because all three bosons hail from the same “Mexican hat”-shaped Brout-Englert-Higgs (BEH) field that broke the electroweak symmetry a fraction of a nanosecond after the Big Bang and left the universe with a non-zero vacuum expectation value. As the universe transitioned from a symmetrical state at the top of the hat to a more stable configuration in the rim, three of the BEH field’s four mathematical components were absorbed to generate masses for the W and Z bosons (while keeping the photon massless); the fourth, corresponding to an otherworldly oscillation up and down the rim of the Mexican hat, is the Higgs boson.</p> <p>In 1983, assuming that the electroweak Standard Model and BEH mechanism were correct, three quarters of the BEH field had been discovered. LEP went on to measure the properties of the W and Z bosons in great detail, helping to constrain the possible hiding places for the “remaining quarter”. The Standard Model does not predict the mass of the Higgs boson. Finding it would require an even more powerful machine. Thanks to the foresight of CERN Director-General John Adams in 1977, the LEP tunnel was designed to be large enough to accommodate the proton–proton collider that, 35 years later, would uncover the final quarter of the mysterious scalar field that pervades the universe and gives mass to elementary particles.</p> <figure class="cds-video" id="CERN-VIDEO-2013-003-001"><div><iframe allowfullscreen="true" frameborder="0" height="450" src="//cds.cern.ch/video/CERN-VIDEO-2013-003-001" width="100%"></iframe></div> <figcaption>The announcement of the W and Z bosons in 1983 <span> (<a href="https://videos.cern.ch/record/1507644">Video: CERN</a>)</span></figcaption></figure> <p> </p> </div> <span><span lang="" about="/user/21331" typeof="schema:Person" property="schema:name" datatype="">thortala</span></span> <span>Wed, 05/25/2022 - 11:18</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="2022-05-25T09:06:24Z">Wed, 05/25/2022 - 11:06</time> </div> </div> Wed, 25 May 2022 09:18:44 +0000 thortala 182616 at https://home.cern CLOUD discovers new way by which aerosols rapidly form and grow at high altitude https://home.cern/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="https://home.cern/science/experiments/cloud">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 class="cds-image" id="CERN-HOMEWEB-PHO-2022-105-1"><a href="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-105-1" title="View on CDS"><img alt="home.cern,Diagrams and Charts" src="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-105-1/file?size=large" /></a> <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><em><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).</em></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.cern ALICE makes first direct observation of a fundamental effect in particle physics https://home.cern/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>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> <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> </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.cern Higgs10: The Higgs boson and the rise of the Standard Model of Particle Physics in the 1970s https://home.cern/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.cern The Higgs boson and the rise of the Standard Model of Particle Physics in the 1970s https://home.cern/news/series/higgs10/higgs-boson-and-rise-standard-model-particle-physics-1970s <div class="layout layout__region featured-story-page-node-layout-content"> <div class="field--items"> <div class="field--item"> <div class="component-row component-row__display__fluid section-navigation component-row__has-header effect_none is_half_height"> <div class="background__veil"></div> <div class="background-component background__cds_media" style="height: 100%;"> <figure class="cds-image" data-record-id="2809116" data-filename="Screenshot%202022-05-10%20at%2016.08.01" id="CERN-HOMEWEB-PHO-2022-081-1"> <a href="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-081-1" title="View on CDS"> <img alt="At Gargamelle with Paul Musset" src="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-081-1/file?size=large"/> </a> <figcaption> At Gargamelle with Paul Musset <span> (Image: CERN)</span> </figcaption> </figure> </div> <div class="component-row__row"> <div class="component-row__column component-row__center section-has-no-column col-md-12 col-sm-12 col-xs-12"> <div class="box-effects-wrapper "> <div class="cern-component-header-blocks component-header"> <div id="header-blocks--2" class="owl-carousel owl-theme component-header__carousel header-carousel"> <div class="header-block"> <div class="header-block__title"> <h3 class="header-block__name" > <span>The Higgs boson and the rise of the Standard Model of Particle Physics in the 1970s</span> <span class="header-block__name__underline"></span> </h3> <span class="header-block__subhead" ><p class="text-align-center">By: <a href="/authors/john-ellis"><span class="cern-tag">John Ellis</span></a></p> <p class="text-align-center">10 May, 2022 · <i>Voir en <a href="/fr/news/series/higgs10/higgs-boson-and-rise-standard-model-particle-physics-1970s">français</a></i></p></span> </div> </div> </div> </div> <a class="endof-cern-header-blocks"></a> </div> </div> </div> </div> </div> <div class="field--item"> <div class="component-row component-row__display__centered section-navigation effect_none"> <div class="component-row__row"> <div class="component-row__column component-row__center section-has-no-column col-md-12 col-sm-12 col-xs-12"> <div class="box-effects-wrapper "> <div class="component-margin component-margin-medium" ></div> <div class="text-component text-component-page clearfix"> <div class="text-component-text cern_full_html"> <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 <a href="/science/physics/standard-model">Standard Model of Particle Physics</a>. As the various breakthroughs of the decade gradually consolidated this theoretical framework, the Brout–Englert–Higgs (BEH) field and its <a href="/science/physics/higgs-boson">boson</a> 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 <a href="/science/experiments/gargamelle">Gargamelle</a> 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 <a href="/news/news/physics/forty-years-neutral-currents">neutral-current discovery</a> convinced physicists that the nascent Standard Model was on the right track. Former CERN Director-General <a href="/about/who-we-are/our-people/biographies/luciano-maiani">Luciano Maiani</a>, quoted in a <a href="https://cerncourier.com/a/neutral-currents-a-perfect-experimental-discovery/">2013 CERN Courier article</a>, puts it this way:</p> <blockquote>"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." –<strong> Luciano Maiani</strong></blockquote> <p class="text-align-right"> </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>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 <a href="/science/physics/w-boson-sunshine-and-stardust">W</a> and <a href="/science/physics/z-boson">Z</a> 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 <a href="/science/accelerators/large-electron-positron-collider">LEP</a> 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> <p>Despite our conviction that something like the Higgs boson had to exist, our <a href="https://cds.cern.ch/record/874049/files/CM-P00061607.pdf">paper</a> ended on a cautionary note that was somewhat tongue-in-cheek:</p> <blockquote>"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."<br /> –<strong> John Ellis, Mary K. Gaillard and Dimitri Nanopoulos</strong></blockquote> <p>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 <a href="/science/accelerators/large-hadron-collider">LHC</a>, focused increasingly on searches for the Higgs boson as the final building block of the Standard Model, culminating in the <a href="/news/press-release/cern/cern-experiments-observe-particle-consistent-long-sought-higgs-boson">discovery on 4 July 2012</a>.</p> </div> </div> </div> </div> </div> </div> </div> <div class="field--item"> As the various breakthroughs of the 1970s gradually consolidated the Standard Model, the Brout–Englert–Higgs field and its boson emerged as the most promising theoretical model to explain the origin of mass </div> </div> </div> Mon, 16 May 2022 12:46:46 +0000 katebrad 182562 at https://home.cern CMS tries out the seesaw https://home.cern/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.cern Higgs10: A boson is born https://home.cern/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.cern A boson is born https://home.cern/news/series/higgs10/boson-born <div class="layout layout__region featured-story-page-node-layout-content"> <div class="field--items"> <div class="field--item"> <div class="component-row component-row__display__fluid section-navigation component-row__has-header effect_none is_half_height"> <div class="background__veil"></div> <div class="background-component background__cds_media" style="height: 100%;"> <figure class="cds-image" data-record-id="1606851" data-filename="Higgsfield" id="OPEN-PHO-ACCEL-2013-052-1"> <a href="//cds.cern.ch/images/OPEN-PHO-ACCEL-2013-052-1" title="View on CDS"> <img alt="Artistic view of the Higgs field" src="//cds.cern.ch/images/OPEN-PHO-ACCEL-2013-052-1/file?size=large"/> </a> <figcaption> A graphic artistic view of the Brout-Englert-Higgs Field <span> (Image: CERN)</span> </figcaption> </figure> </div> <div class="component-row__row"> <div class="component-row__column component-row__center section-has-no-column col-md-12 col-sm-12 col-xs-12"> <div class="box-effects-wrapper "> <div class="cern-component-header-blocks component-header"> <div id="header-blocks--4" class="owl-carousel owl-theme component-header__carousel header-carousel"> <div class="header-block"> <div class="header-block__title"> <h3 class="header-block__name" > <span>A boson is born</span> <span class="header-block__name__underline"></span> </h3> <span class="header-block__subhead" ><p class="text-align-center">By: <a href="/authors/matthew-chalmers"><span class="cern-tag">Matthew Chalmers</span></a></p> <p class="text-align-center">28 April, 2022 · <i>Voir en <a href="/fr/news/series/higgs10/boson-born">français</a></i></p> <hr /> <p class="text-align-center">In the first part of the <a href="/news/series/higgs10"><span class="cern-tag">Higgs10</span></a> series, we look at the how the Higgs boson came to be</p> </span> </div> </div> </div> </div> <a class="endof-cern-header-blocks"></a> </div> </div> </div> </div> </div> <div class="field--item"> <div class="component-row component-row__display__centered section-navigation effect_none"> <div class="component-row__row"> <div class="component-row__column component-row__center section-has-no-column col-md-12 col-sm-12 col-xs-12"> <div class="box-effects-wrapper "> <div class="component-margin component-margin-medium" ></div> <div class="text-component text-component-page clearfix"> <div class="text-component-text cern_full_html"> <p><strong><em>On 4 July 2012, half a century’s wait came to an end as the <a href="/science/experiments/atlas">ATLAS</a> and <a href="/science/experiments/cms">CMS</a> experiments announced the discovery of the <a href="/science/physics/higgs-boson">Higgs boson</a>. </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 “Higgs10” series 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> <figure class="cds-image align-right" id="CERN-HI-1207136-101"><a href="//cds.cern.ch/images/CERN-HI-1207136-101" title="View on CDS"><img alt="higgsjuly4,seminar,Milestones,Higgs Boson Discovery,360" src="//cds.cern.ch/images/CERN-HI-1207136-101/file?size=large" /></a> <figcaption>Theoretical physicists François Englert (left) and Peter Higgs at CERN on 4 July 2012, at the announcement of the discovery of a Higgs boson by the ATLAS and CMS experiments. <span> (Image: M. Brice/CERN)</span></figcaption></figure> <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> <figure class="cds-image align-right" id="CERN-HOMEWEB-PHO-2022-071-1"><a href="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-071-1" title="View on CDS"><img alt="home.cern,Miscellaneous" src="//cds.cern.ch/images/CERN-HOMEWEB-PHO-2022-071-1/file?size=large" /></a> <figcaption>The 1964 Peter Higgs paper that first predicted the existence of what would come to be known as the Higgs boson. (Image: paper, APS; logo, CERN)</figcaption></figure> <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> <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, <a href="https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.13.508">Higgs’ second paper</a> was received and accepted the same day (31 August 1964) that <em>Physical Review Letters</em> published <a href="https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.13.321">Brout and Englert’s similarly titled work</a>. 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> <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>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><a href="https://home.cern/news/press-release/cern/cern-experiments-observe-particle-consistent-long-sought-higgs-boson">The discovery of the Higgs boson at the LHC in 2012</a> 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> </div> </div> </div> </div> </div> </div> <div class="field--item"> 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 </div> </div> </div> Mon, 09 May 2022 11:38:08 +0000 katebrad 182526 at https://home.cern CMS measures the mass of the top quark with unparalleled accuracy https://home.cern/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.cern LHCb reveals secret of antimatter creation in cosmic collisions https://home.cern/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.cern