Search for flavour-changing neutral-current couplings between the top quark and the photon with the ATLAS detector at s=13 TeV

The ATLAS collaboration

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Abstract

This letter documents a search for flavour-changing neutral currents (FCNCs), which are strongly suppressed in the Standard Model, in events with a photon and a top quark with the ATLAS detector. The analysis uses data collected in pp collisions at s=13 TeV during Run 2 of the LHC, corresponding to an integrated luminosity of 139 fb−1. Both FCNC top-quark production and decay are considered. The final state consists of a charged lepton, missing transverse momentum, a b-tagged jet, one high-momentum photon and possibly additional jets. A multiclass deep neural network is used to classify events either as signal in one of the two categories, FCNC production or decay, or as background. No significant excess of events over the background prediction is observed and 95% CL upper limits are placed on the strength of left- and right-handed FCNC interactions. The 95% CL bounds on the branching fractions for the FCNC top-quark decays, estimated (expected) from both top-quark production and decay, are B(t→uγ)<0.85(0.88−0.25 +0.37)×10−5 and B(t→cγ)<4.2(3.40−0.95 +1.35)×10−5 for a left-handed tqγ coupling, and B(t→uγ)<1.2(1.20−0.33 +0.50)×10−5 and B(t→cγ)<4.5(3.70−1.03 +1.47)×10−5 for a right-handed coupling.

Original languageEnglish
Article number137379
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Volume842
DOIs
StatePublished - 10 Jul 2023

Funding

FundersFunder number
CEA-DRF
Canton of Bern and Geneva
DNSRCIN2P3-CNRS
EU-ESF
GenT Programmes Generalitat Valenciana , Spain
GenT Programmes Generalitat Valenciana, Spain
GridKA
INFN-CNAF
La Caixa Banking Foundation
MIZŠ
MNE
NDGFCC-IN2P3
Norwegian Financial Mechanism2014-2021
PROMETEO
RGC
UNCESCI/013
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
CERN
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
Helmholtz-Gemeinschaft
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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