{"id":23842,"date":"2023-03-23T21:14:41","date_gmt":"2023-03-23T15:29:41","guid":{"rendered":"https:\/\/www.revoscience.com\/en\/?p=23842"},"modified":"2023-03-23T21:16:00","modified_gmt":"2023-03-23T15:31:00","slug":"improved-atlas-result-weighs-in-on-the-w-boson","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/improved-atlas-result-weighs-in-on-the-w-boson\/","title":{"rendered":"Improved ATLAS result weighs in on the W boson<\/strong>"},"content":{"rendered":"\n

Geneva\u2014The\u00a0W boson<\/a>, a fundamental particle that carries the charged weak force, is the subject of a new precision measurement of its mass by the\u00a0ATLAS<\/a>\u00a0experiment at CERN.<\/p>\n\n\n\n

The preliminary result, reported in a new\u00a0conference note<\/a>\u00a0presented today at the\u00a0Rencontres de Moriond<\/a>\u00a0conference, is based on a reanalysis of a sample of 14 million W boson candidates produced in proton\u2013proton collisions at the\u00a0Large Hadron Collider<\/a>\u00a0(LHC), CERN\u2019s flagship particle accelerator.<\/p>\n\n\n\n

The new ATLAS measurement concurs with and is more precise than, all previous W mass measurements except one \u2013 the latest measurement from the CDF experiment at the\u00a0Tevatron<\/a>, a former accelerator at Fermilab.<\/p>\n\n\n\n

\"\"
Event display of a W-boson candidate decaying into a muon and a muon neutrino inside the ATLAS\u00a0experiment. The blue line shows the reconstructed\u00a0track\u00a0of the muon,\u00a0and the red arrow denotes\u00a0the\u00a0energy of the undetected\u00a0muon neutrino\u00a0(Image<\/strong>: CERN)<\/figcaption><\/figure>\n\n\n\n

Together with its electrically neutral counterpart, the Z boson<\/a>, the electrically charged W boson mediates the weak force, a fundamental force that is responsible for a form of radioactivity and initiates the nuclear fusion reaction that powers the Sun.<\/p>\n\n\n\n

The particle\u2019s discovery at CERN 40 years ago<\/a> helped to confirm the theory of the electroweak interaction that unifies the electromagnetic and weak forces. This theory is now a cornerstone of the Standard Model<\/a> of particle physics. CERN researchers who enabled the discovery were awarded the 1984 Nobel Prize in physics<\/a>.<\/p>\n\n\n\n

Since then, experiments at particle colliders at CERN and elsewhere have measured the W boson mass ever more precisely. In the Standard Model, the W boson mass is closely related to the strength of the electroweak interactions and the masses of the heaviest fundamental particles, including the Z boson, the top quark, and the\u00a0Higgs boson<\/a>. In this theory, the particle is constrained to weigh 80354 million electronvolts (MeV), within an uncertainty of 7 MeV.<\/p>\n\n\n\n

Any deviation of the measured mass from the Standard Model prediction would be an indicator of new physics phenomena, such as new particles or interactions. To be sensitive to such deviations, mass measurements need to be extremely precise.<\/p>\n\n\n\n

In 2017, ATLAS released its first measurement of the W boson mass<\/a>, which was determined using a sample of W bosons recorded by ATLAS in 2011, when the LHC was running at a collision energy of 7 TeV. The W boson mass came out at 80370 MeV, with an uncertainty of 19 MeV.<\/p>\n\n\n\n

At the time, this result represented the most precise W boson mass value ever obtained by a single experiment and was in good agreement with the Standard Model prediction and all previous experimental results, including those\u00a0from experiments at the\u00a0Large Electron-Positron Collider<\/a>\u00a0(LEP), the LHC\u2019s predecessor at CERN.<\/p>\n\n\n\n

Last year, the CDF collaboration at Fermilab announced an even more precise measurement, based on an analysis of its full dataset collected at the Tevatron. The result, 80434 MeV with an uncertainty of 9 MeV, differed significantly from the Standard Model prediction and from the other experimental results, calling for more measurements to try to identify the cause of the difference.<\/p>\n\n\n\n

In its new study, ATLAS reanalyzed its 2011 sample of W bosons,\u00a0improving the precision of its previous measurement. The new W boson mass, 80360 MeV with an uncertainty of 16 MeV, is 10 MeV lower than the previous ATLAS result and 16% more precise. The result is in agreement with the Standard Model.<\/p>\n\n\n\n

\"\"
Comparison of the measured value of the W boson mass with other published results. The vertical bands show the Standard Model prediction, and the horizontal bands and lines show the statistical and total uncertainties of the results (Image:<\/strong> CERN)<\/em><\/figcaption><\/figure>\n\n\n\n

To attain this result, ATLAS used an advanced data-fitting technique to determine the mass, as well as more recent, improved versions of what is known as the\u00a0parton distribution functions of the proton. These functions\u00a0describe\u00a0the sharing of the proton\u2019s momentum amongst its constituent quarks and gluons. In addition, ATLAS verified the theoretical description of the W boson production process using dedicated LHC proton\u2013proton runs.<\/p>\n\n\n\n

\u201cDue to an undetected neutrino in the particle\u2019s decay,\u00a0the W mass measurement is among the most challenging precision measurements performed at hadron colliders. It requires extremely accurate calibration of the measured particle energies and momenta, and a careful assessment and excellent control of modeling uncertainties,\u201d says ATLAS spokesperson Andreas Hoecker. \u201cThis updated result from ATLAS provides a stringent test, and confirms the consistency of our theoretical understanding of electroweak interactions.\u201d<\/p>\n\n\n\n

Further measurements of the W boson mass are expected from ATLAS and\u00a0CMS<\/a>\u00a0and from\u00a0LHCb<\/a>, which has also recently\u00a0weighed<\/a>\u00a0the boson. <\/p>\n","protected":false},"excerpt":{"rendered":"

The\u00a0W boson, a fundamental particle that carries the charged weak force, is the subject of a new precision measurement of its mass by the\u00a0ATLAS\u00a0experiment at CERN.<\/p>\n","protected":false},"author":2,"featured_media":23844,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[],"class_list":["post-23842","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news"],"featured_image_urls":{"full":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon.png",640,640,false],"thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon-200x200.png",200,200,true],"medium":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon-400x400.png",400,400,true],"medium_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon.png",640,640,false],"large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon.png",640,640,false],"1536x1536":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon.png",640,640,false],"2048x2048":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon.png",640,640,false],"ultp_layout_landscape_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon.png",640,640,false],"ultp_layout_landscape":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon-640x570.png",640,570,true],"ultp_layout_portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon-600x640.png",600,640,true],"ultp_layout_square":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon-600x600.png",600,600,true],"newspaper-x-single-post":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon-640x490.png",640,490,true],"newspaper-x-recent-post-big":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon-550x360.png",550,360,true],"newspaper-x-recent-post-list-image":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon-95x65.png",95,65,true],"web-stories-poster-portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon.png",640,640,false],"web-stories-publisher-logo":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon.png",96,96,false],"web-stories-thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2023\/03\/W-boson-candidate-decaying-into-a-muon.png",150,150,false]},"author_info":{"info":["RevoScience"]},"category_info":"News<\/a>","tag_info":"News","comment_count":"0","_links":{"self":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/23842","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/comments?post=23842"}],"version-history":[{"count":0,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/23842\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media\/23844"}],"wp:attachment":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media?parent=23842"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/categories?post=23842"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/tags?post=23842"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}