Measurement of the polarisation of W bosons produced in top-quark decays using dilepton events at s=13 TeV with the ATLAS experiment

The ATLAS collaboration

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A measurement of the polarisation of W bosons produced in top-quark decays is presented, using proton–proton collision data at a centre-of-mass energy of s=13 TeV. The data were collected by the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 139 fb−1. The measurement is performed selecting tt¯ events decaying into final states with two charged leptons (electrons or muons) and at least two b-tagged jets. The polarisation is extracted from the differential cross-section distribution of the cos⁡θ variable, where θ is the angle between the momentum direction of the charged lepton from the W boson decay and the reversed momentum direction of the b-quark from the top-quark decay, both calculated in the W boson rest frame. Parton-level results, corrected for the detector acceptance and resolution, are presented for the cos⁡θ angle. The measured fractions of longitudinal, left- and right-handed polarisation states are found to be f0=0.684±0.005(stat.)±0.014(syst.), fL=0.318±0.003(stat.)±0.008(syst.) and fR=−0.002±0.002(stat.)±0.014(syst.), in agreement with the Standard Model prediction.

Original languageEnglish
Article number137829
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
StatePublished - 10 Aug 2023


FundersFunder number
Cantons of Bern and Geneva
GenT Programmes Generalitat Valenciana , Spain
GenT Programmes Generalitat Valenciana, Spain
La Caixa Banking Foundation
Norwegian Financial Mechanism2014-2021
Wallenberg Foundation
National Science Foundation
U.S. Department of Energy
Alexander von Humboldt-Stiftung
Alabama Space Grant Consortium
Brookhaven National Laboratory
Karlsruhe Institute of Technology
H2020 Marie Skłodowska-Curie Actions
Multiple Sclerosis Scientific Research Foundation
Göran Gustafssons Stiftelser
Natural Sciences and Engineering Research Council of Canada
National Research Council Canada
Canada Foundation for Innovation
Science and Technology Facilities Council
Leverhulme Trust
European Research Council
European Cooperation in Science and Technology
Australian Research Council
National Stroke Foundation
Neurosurgical Research Foundation
Minerva Foundation
Deutsche Forschungsgemeinschaft
Agence Nationale de la Recherche
Japan Society for the Promotion of Science
Ministry of Education, Culture, Sports, Science and Technology
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
Danmarks Grundforskningsfond
Fundação de Amparo à Pesquisa do Estado de São Paulo
National Natural Science Foundation of China
Ministerstvo Školství, Mládeže a Tělovýchovy
Fundação para a Ciência e a Tecnologia
Bundesministerium für Bildung und Forschung
Chinese Academy of Sciences
Austrian Science Fund
Generalitat de Catalunya
Ministry of Science and Technology of the People's Republic of China
Agencia Nacional de Promoción Científica y Tecnológica
Nederlandse Organisatie voor Wetenschappelijk Onderzoek
Bundesministerium für Wissenschaft, Forschung und Wirtschaft
Conselho Nacional de Desenvolvimento Científico e Tecnológico
Nella and Leon Benoziyo Center for Neurological Diseases, Weizmann Institute of Science
Israel Science Foundation
Instituto Nazionale di Fisica Nucleare
Narodowe Centrum Nauki
Javna Agencija za Raziskovalno Dejavnost RS
Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja
Ministerio de Ciencia e Innovación
Centre National pour la Recherche Scientifique et Technique
Staatssekretariat für Bildung, Forschung und Innovation
Horizon 2020
British Columbia Knowledge Development Fund21/SCI/017
European Regional Development Fund
Defence Science Institute
Narodowa Agencja Wymiany Akademickiej
Institutul de Fizică Atomică
Agencia Nacional de Investigación y Desarrollo
Royal Society of South Australia
Irish Rugby Football Union


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