CMS uses photons to probe the structure of nuclei

<!DOCTYPE html> <html lang="en" dir="ltr" prefix="content: http://purl.org/rss/1.0/modules/content/ dc: http://purl.org/dc/terms/ foaf: http://xmlns.com/foaf/0.1/ og: http://ogp.me/ns# rdfs: http://www.w3.org/2000/01/rdf-schema# schema: http://schema.org/ sioc: http://rdfs.org/sioc/ns# sioct: http://rdfs.org/sioc/types# skos: http://www.w3.org/2004/02/skos/core# xsd: http://www.w3.org/2001/XMLSchema# "> <head> <meta charset="utf-8" /> <script>var _paq = _paq || [];(function(){var u=(("https:" == document.location.protocol) ? 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As a result, photons from the oncoming lead-ion beams can interact with each other or with the nuclei; these interactions are known as ultraperipheral collisions. Photon–nucleus scatterings at the highest energy that can be achieved with existing particle accelerators are useful probes that allow physicists to investigate the structure of nuclei. While the common picture of nucleons is that they contain three quarks (up–up–down for protons and up–down–down for neutrons), in reality, a complex sea consisting of quark–antiquark pairs and gluons makes up a large fraction of the proton and neutron energies. Ultraperipheral collisions are an extraordinary tool to test the nature of nuclear matter. The CMS experiment has recently released the first results using data from the first heavy-ion run of LHC Run 3. The results measure the production of D0 mesons (containing a charm quark and an up antiquark) and their antiparticles, D0 bar mesons (made of an up quark and a charm antiquark), in ultraperipheral collisions for the first time. D0 mesons are formed by charm quarks that are kicked out of the nuclei by the photons and carry information about parton distribution functions, which describe how quarks and gluons behave inside nuclei. To measure D0 production, the CMS detector first selects events in which photon and lead nuclei collisions have caused the latter to break up. When this happens, neutrons flow from the collision in parallel to the beam, whereas protons and intact nuclei will follow a curved path as their charge interacts with the LHC’s magnetic fields. Two calorimeters, at zero degrees to the beam and located 140 m away on either side of the interaction point, are able to detect such neutrons. If they are seen in one calorimeter and not the other, in a time window consistent with the collision, this event is selected for further investigation. Then, the products of the D0 decay – oppositely charged kaon and pion pairs – are reconstructed in the CMS detector. Physicists consider all combinations of pion and kaon trajectories, with each track taking an assumed mass of the kaon and pion. They then filter these combinations using the data to identify tracks that match what they expect from a D0 meson. From this, they are able to measure the so-called production cross section, which is the rate at which D0 mesons are produced. For CMS, the study of nuclear structure using D0 meson production is just one of many applications of ultraperipheral collisions. With time, as methods are refined and systematic uncertainties are reduced, this technique will be able to constrain the parton distribution functions, allowing physicists to understand the structure of nuclear matter more deeply. The next heavy-ion run of LHC Run 3 will start at the beginning of November. Read more: CMS briefing Paper" /> <meta property="og:image" content="https://cds.cern.ch/images//file?size=medium" /> <meta name="twitter:card" content="summary_large_image" /> <meta name="twitter:description" content="At the Large Hadron Collider (LHC), heavy ions are accelerated to extremely high energies, which creates strong electromagnetic fields. As a result, photons from the oncoming lead-ion beams can interact with each other or with the nuclei; these interactions are known as ultraperipheral collisions. Photon–nucleus scatterings at the highest energy that can be achieved with existing particle accelerators are useful probes that allow physicists to investigate the structure of nuclei. While the common picture of nucleons is that they contain three quarks (up–up–down for protons and up–down–down for neutrons), in reality, a complex sea consisting of quark–antiquark pairs and gluons makes up a large fraction of the proton and neutron energies. Ultraperipheral collisions are an extraordinary tool to test the nature of nuclear matter. The CMS experiment has recently released the first results using data from the first heavy-ion run of LHC Run 3. The results measure the production of D0 mesons (containing a charm quark and an up antiquark) and their antiparticles, D0 bar mesons (made of an up quark and a charm antiquark), in ultraperipheral collisions for the first time. D0 mesons are formed by charm quarks that are kicked out of the nuclei by the photons and carry information about parton distribution functions, which describe how quarks and gluons behave inside nuclei. To measure D0 production, the CMS detector first selects events in which photon and lead nuclei collisions have caused the latter to break up. When this happens, neutrons flow from the collision in parallel to the beam, whereas protons and intact nuclei will follow a curved path as their charge interacts with the LHC’s magnetic fields. Two calorimeters, at zero degrees to the beam and located 140 m away on either side of the interaction point, are able to detect such neutrons. If they are seen in one calorimeter and not the other, in a time window consistent with the collision, this event is selected for further investigation. Then, the products of the D0 decay – oppositely charged kaon and pion pairs – are reconstructed in the CMS detector. Physicists consider all combinations of pion and kaon trajectories, with each track taking an assumed mass of the kaon and pion. They then filter these combinations using the data to identify tracks that match what they expect from a D0 meson. From this, they are able to measure the so-called production cross section, which is the rate at which D0 mesons are produced. For CMS, the study of nuclear structure using D0 meson production is just one of many applications of ultraperipheral collisions. With time, as methods are refined and systematic uncertainties are reduced, this technique will be able to constrain the parton distribution functions, allowing physicists to understand the structure of nuclear matter more deeply. The next heavy-ion run of LHC Run 3 will start at the beginning of November. Read more: CMS briefing Paper" /> <meta name="twitter:site" content="@cern" /> <meta name="twitter:title" content="CMS uses photons to probe the structure of nuclei" /> <meta name="twitter:image" content="https://cds.cern.ch/images//file?size=medium" /> <meta name="Generator" content="Drupal 10 (https://www.drupal.org)" /> <meta name="MobileOptimized" content="width" /> <meta name="HandheldFriendly" content="true" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <link rel="icon" href="/sites/default/themes/custom/cernpublic/favicon.ico" type="image/vnd.microsoft.icon" /> <link rel="alternate" hreflang="en" href="https://home.cern/news/news/physics/cms-uses-photons-probe-structure-nuclei" /> <link rel="alternate" hreflang="fr" href="https://home.cern/fr/news/news/physics/cms-uses-photons-probe-structure-nuclei" /> <title>CMS uses photons to probe the structure of nuclei | CERN</title> <link rel="stylesheet" media="all" 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(Image: CMS collaboration) </caption> </p> <div class="news-node-full-content-body clearfix full-html-markup full-text-animation"> <p>At the Large Hadron Collider (<a href="https://home.cern/science/accelerators/large-hadron-collider">LHC</a>), heavy ions are accelerated to extremely high energies, which creates strong electromagnetic fields. As a result, photons from the oncoming lead-ion beams can interact with each other or with the nuclei; these interactions are known as ultraperipheral collisions. Photon–nucleus scatterings at the highest energy that can be achieved with existing particle accelerators are useful probes that allow physicists to investigate the structure of nuclei. While the common picture of nucleons is that they contain three quarks (up–up–down for protons and up–down–down for neutrons), in reality, a complex sea consisting of quark–antiquark pairs and gluons makes up a large fraction of the proton and neutron energies. Ultraperipheral collisions are an extraordinary tool to test the nature of nuclear matter.</p> <p>The <a href="https://home.cern/science/experiments/cms">CMS experiment</a> has recently released the first <a href="https://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/HIN-24-003/index.html">results</a> using data from the first <a href="https://home.cern/science/physics/heavy-ions-and-quark-gluon-plasma">heavy-ion</a> run of LHC Run 3. The results measure the production of D<sup>0</sup> mesons (containing a charm quark and an up antiquark) and their antiparticles, D<sup>0</sup> bar mesons (made of an up quark and a charm antiquark), in ultraperipheral collisions for the first time. D<sup>0</sup> mesons are formed by charm quarks that are kicked out of the nuclei by the photons and carry information about parton distribution functions, which describe how quarks and gluons behave inside nuclei.</p> <p>To measure D<sup>0</sup> production, the CMS detector first selects events in which photon and lead nuclei collisions have caused the latter to break up. When this happens, neutrons flow from the collision in parallel to the beam, whereas protons and intact nuclei will follow a curved path as their charge interacts with the LHC’s magnetic fields. Two calorimeters, at zero degrees to the beam and located 140 m away on either side of the interaction point, are able to detect such neutrons. If they are seen in one calorimeter and not the other, in a time window consistent with the collision, this event is selected for further investigation.</p> <p>Then, the products of the D<sup>0</sup> decay – oppositely charged kaon and pion pairs – are reconstructed in the CMS detector. Physicists consider all combinations of pion and kaon trajectories, with each track taking an assumed mass of the kaon and pion. They then filter these combinations using the data to identify tracks that match what they expect from a D<sup>0</sup> meson. From this, they are able to measure the so-called production cross section, which is the rate at which D<sup>0</sup> mesons are produced.</p> <p>For CMS, the study of nuclear structure using D<sup>0</sup> meson production is just one of many applications of ultraperipheral collisions. With time, as methods are refined and systematic uncertainties are reduced, this technique will be able to constrain the parton distribution functions, allowing physicists to understand the structure of nuclear matter more deeply.</p> <p><em>The next heavy-ion run of LHC Run 3 will start at the beginning of November.</em></p> <hr> <p><strong>Read more:</strong></p> <ul> <li><a href="https://cms.cern/news/charming-look-structure-nuclei-using-collisions-photon-clouds">CMS briefing</a></li> <li><a href="https://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/HIN-24-003/index.html">Paper</a></li> </ul> </div> <div class="news-node-full-content-tags "> <a href="/tags/heavy-ion" hreflang="en">heavy ion</a> </div> </div> </div> </div> </div> <div class="sidebar-right col-md-3 col-sm-12 col-xs-12"> <div class="region region-right"> <section class="views-element-container block block-views block-views-blocknews-microviews-block-12 clearfix" 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