CERN: Physics updates https://home.cern/ en 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_full_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_full_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> <span class="component-header__scroll"></span> </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 ATLAS strengthens its search for supersymmetry https://home.cern/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.cern MoEDAL gets a new detector https://home.cern/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.cern Mass matters when quarks cross a quark–gluon plasma https://home.cern/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.cern