Test of the universality of τ and μ lepton couplings in W-boson decays with the ATLAS detector

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[1] Aix-Marseille Université,CPPM
[2] CNRS/IN2P3,Homer L. Dodge Department of Physics and Astronomy
[3] University of Oklahoma,Department of Physics
[4] University of Massachusetts,II. Physikalisches Institut
[5] CERN,Department of Physics
[6] Georg-August-Universität Göttingen,Department of Physics
[7] Royal Holloway University of London,Niels Bohr Institute
[8] University of Toronto,Department of Physics and Astronomy
[9] University of Copenhagen,Raymond and Beverly Sackler School of Physics and Astronomy
[10] University of Sussex,Department of Physics
[11] Tel Aviv University,High Energy Physics Division
[12] Technion,INFN Gruppo Collegato di Udine
[13] Israel Institute of Technology,Institut für Physik
[14] Argonne National Laboratory,LAPP
[15] Sezione di Trieste,AGH University of Science and Technology
[16] ICTP,Department of Physics
[17] Universität Mainz,Fakultät für Physik
[18] Université Grenoble Alpes,Department of Physics
[19] Université Savoie Mont Blanc,Département de Physique Nucléaire et Corpusculaire
[20] CNRS/IN2P3,Particle Physics Department
[21] Faculty of Physics and Applied Computer Science,Santa Cruz Institute for Particle Physics
[22] Northern Illinois University,IJCLab
[23] Ludwig-Maximilians-Universität München,LPC
[24] Bogazici University,Institute for Mathematics, Astrophysics and Particle Physics
[25] Université de Genève,Department of Physics
[26] Rutherford Appleton Laboratory,Departamento de Física Teórica y del Cosmos
[27] University of California Santa Cruz,Department of Physics
[28] Université Paris-Saclay,Dipartimento di Fisica
[29] CNRS/IN2P3,Faculty of Science
[30] 91405,Fysiska Institutionen
[31] Université Clermont Auvergne,Dipartimento di Fisica
[32] CNRS/IN2P3,Department of Physics and Astronomy
[33] Radboud University/Nikhef,Physics Department
[34] Alexandru Ioan Cuza University of Iasi,Institute of Physics
[35] Laboratório de Instrumentação e Física Experimental de Partículas – LIP,Institute for Fundamental Science
[36] Universidad de Granada,School of Physics and Astronomy
[37] Joint Institute for Nuclear Research,Dipartimento di Fisica
[38] McGill University,Instituto de Física La Plata
[39] Physics Division,Department of Physics
[40] Lawrence Berkeley National Laboratory and University of California,Departamento de Física Teorica C
[41] INFN Sezione di Roma Tor Vergata,15 and CIAFF
[42] Università di Roma Tor Vergata,Department of Physics
[43] Kyoto University,Department of Physics
[44] Lunds Universitet,Department of Physics
[45] P.N. Lebedev Physical Institute of the Russian Academy of Sciences,Department of Physics and Astronomy
[46] INFN Bologna and Università di Bologna,Department of Physics and Astronomy
[47] INFN Sezione di Bologna,IRFU, CEA
[48] University of Victoria,Department of Physics
[49] Horia Hulubei National Institute of Physics and Nuclear Engineering,Albert Einstein Center for Fundamental Physics and Laboratory for High Energy Physics
[50] National Technical University of Athens,Department of Physics
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Nature Physics | 2021年 / 17卷
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The standard model of particle physics encapsulates our best current understanding of physics at the smallest scales. A fundamental axiom of this theory is the universality of the couplings of the different generations of leptons to the electroweak gauge bosons. The measurement of the ratio of the decay rate of W bosons to τ leptons and muons, R(τ/μ), constitutes an important test of this axiom. Using 139 fb−1 of proton–proton collisions recorded with the ATLAS detector at a centre-of-mass energy of 13 TeV, we report a measurement of this quantity from di-leptonic tt¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$t\overline{t}$$\end{document} events where the top quarks decay into a W boson and a bottom quark. We can distinguish muons originating from W bosons and those originating from an intermediate τ lepton through the muon transverse impact parameter and differences in the muon transverse momentum spectra. The measured value of R(τ/μ) is 0.992 ± 0.013 [± 0.007(stat) ± 0.011(syst)] and is in agreement with the hypothesis of universal lepton couplings as postulated in the standard model. This is the only such measurement from the Large Hadron Collider, so far, and obtains twice the precision of previous measurements.
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页码：813 / 818
页数：5
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