Eur. Phys. J. C (2025) 85: 153
https://doi.org/10.1140/epjc/s10052-024-13715-4

Regular Article - Experimental Physics

Search for a light charged Higgs boson in $t\to H^{\pm }b$ decays, with $H^{\pm }\to cs$, in $\mathit{pp}$ collisions at $\sqrt{s}=13\text{TeV}$ with the ATLAS detector

¹ Department of Physics, University of Adelaide, Adelaide, Australia
² Department of Physics, University of Alberta, Edmonton, AB, Canada
³ Department of Physics, Ankara University, Ankara, Turkey
⁴ Division of Physics, TOBB University of Economics and Technology, Ankara, Turkey
⁵ LAPP, Université Savoie Mont Blanc, CNRS/IN2P3, Annecy, France
⁶ APC, Université Paris Cité, CNRS/IN2P3, Paris, France
⁷ High Energy Physics Division, Argonne National Laboratory, Argonne, IL, USA
⁸ Department of Physics, University of Arizona, Tucson, AZ, USA
⁹ Department of Physics, University of Texas at Arlington, Arlington, TX, USA
¹⁰ Physics Department, National and Kapodistrian University of Athens, Athens, Greece
¹¹ Physics Department, National Technical University of Athens, Zografou, Greece
¹² Department of Physics, University of Texas at Austin, Austin, TX, USA
¹³ Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan
¹⁴ Institut de Física d’Altes Energies (IFAE), Barcelona Institute of Science and Technology, Barcelona, Spain
¹⁵ Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
¹⁶ Physics Department, Tsinghua University, Beijing, China
¹⁷ Institute of Physics, University of Belgrade, Belgrade, Serbia
¹⁸ Department for Physics and Technology, University of Bergen, Bergen, Norway
¹⁹ Physics Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
²⁰ University of California, Berkeley, CA, USA
²¹ Institut für Physik, Humboldt Universität zu Berlin, Berlin, Germany
²² Albert Einstein Center for Fundamental Physics and Laboratory for High Energy Physics, University of Bern, Bern, Switzerland
²³ School of Physics and Astronomy, University of Birmingham, Birmingham, UK
²⁴ Department of Physics, Bogazici University, Istanbul, Turkey
²⁵ Department of Physics Engineering, Gaziantep University, Gaziantep, Turkey
²⁶ Department of Physics, Istanbul University, Istanbul, Turkey
²⁷ Facultad de Ciencias y Centro de Investigaciónes, Universidad Antonio Nariño, Bogotá, Colombia
²⁸ Departamento de Física, Universidad Nacional de Colombia, Bogotá, Colombia
²⁹ Dipartimento di Fisica e Astronomia A. Righi, Universitá di Bologna, Bologna, Italy
³⁰ INFN Sezione di Bologna, Bologna, Italy
³¹ Physikalisches Institut, Universität Bonn, Bonn, Germany
³² Department of Physics, Boston University, Boston, MA, USA
³³ Department of Physics, Brandeis University, Waltham, MA, USA
³⁴ Transilvania University of Brasov, Brasov, Romania
³⁵ Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania
³⁶ Department of Physics, Alexandru Ioan Cuza University of Iasi, Iasi, Romania
³⁷ National Institute for Research and Development of Isotopic and Molecular Technologies, Physics Department, Cluj-Napoca, Romania
³⁸ National University of Science and Technology Politechnica, Bucharest, Romania
³⁹ West University in Timisoara, Timisoara, Romania
⁴⁰ Faculty of Physics, University of Bucharest, Bucharest, Romania
⁴¹ Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
⁴² Department of Subnuclear Physics, Institute of Experimental Physics of the Slovak Academy of Sciences, Kosice, Slovak Republic
⁴³ Physics Department, Brookhaven National Laboratory, Upton, NY, USA
⁴⁴ Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Física, y CONICET, Instituto de Físca de Buenos Aires (IFIBA), Buenos Aires, Argentina
⁴⁵ California State University, Los Angeles, CA, USA
⁴⁶ Cavendish Laboratory, University of Cambridge, Cambridge, UK
⁴⁷ Department of Physics, University of Cape Town, Cape Town, South Africa
⁴⁸ iThemba Labs, Western Cape, South Africa
⁴⁹ Department of Mechanical Engineering Science, University of Johannesburg, Johannesburg, South Africa
⁵⁰ National Institute of Physics, University of the Philippines Diliman (Philippines), Quezon City, Philippines
⁵¹ University of South Africa, Department of Physics, Pretoria, South Africa
⁵² University of Zululand, KwaDlangezwa, South Africa
⁵³ School of Physics, University of the Witwatersrand, Johannesburg, South Africa
⁵⁴ Department of Physics, Carleton University, Ottawa, ON, Canada
⁵⁵ Faculté des Sciences Ain Chock, Université Hassan II de Casablanca, Casablanca, Morocco
⁵⁶ Faculté des Sciences, Université Ibn-Tofail, Kénitra, Morocco
⁵⁷ Faculté des Sciences Semlalia, Université Cadi Ayyad, LPHEA-Marrakech, Marrakech, Morocco
⁵⁸ LPMR, Faculté des Sciences, Université Mohamed Premier, Oujda, Morocco
⁵⁹ Faculté des sciences, Université Mohammed V, Rabat, Morocco
⁶⁰ Institute of Applied Physics, Mohammed VI Polytechnic University, Ben Guerir, Morocco
⁶¹ CERN, Geneva, Switzerland
⁶² Affiliated with an institute covered by a cooperation agreement with CERN, Geneva, Switzerland
⁶³ Affiliated with an international laboratory covered by a cooperation agreement with CERN, Geneva, Switzerland
⁶⁴ Enrico Fermi Institute, University of Chicago, Chicago, IL, USA
⁶⁵ LPC, Université Clermont Auvergne, CNRS/IN2P3, Clermont-Ferrand, France
⁶⁶ Nevis Laboratory, Columbia University, Irvington, NY, USA
⁶⁷ Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
⁶⁸ Dipartimento di Fisica, Università della Calabria, Rende, Italy
⁶⁹ INFN Gruppo Collegato di Cosenza, Laboratori Nazionali di Frascati, Italy
⁷⁰ Physics Department, Southern Methodist University, Dallas, TX, USA
⁷¹ Physics Department, University of Texas at Dallas, Richardson, TX, USA
⁷² National Centre for Scientific Research “Demokritos”, Agia Paraskevi, Greece
⁷³ Department of Physics, Stockholm University, Stockholm, Sweden
⁷⁴ Oskar Klein Centre, Stockholm, Sweden
⁷⁵ Deutsches Elektronen-Synchrotron DESY, Hamburg and Zeuthen, Germany
⁷⁶ Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany
⁷⁷ Institut für Kern- und Teilchenphysik, Technische Universität Dresden, Dresden, Germany
⁷⁸ Department of Physics, Duke University, Durham, NC, USA
⁷⁹ SUPA-School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK
⁸⁰ INFN e Laboratori Nazionali di Frascati, Frascati, Italy
⁸¹ Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
⁸² II. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen, Germany
⁸³ Département de Physique Nucléaire et Corpusculaire, Université de Genève, Geneva, Switzerland
⁸⁴ Dipartimento di Fisica, Università di Genova, Genoa, Italy
⁸⁵ INFN Sezione di Genova, Genoa, Italy
⁸⁶ II. Physikalisches Institut, Justus-Liebig-Universität Giessen, Giessen, Germany
⁸⁷ SUPA-School of Physics and Astronomy, University of Glasgow, Glasgow, UK
⁸⁸ LPSC, Université Grenoble Alpes, CNRS/IN2P3, Grenoble INP, Grenoble, France
⁸⁹ Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge, MA, USA
⁹⁰ Department of Modern Physics and State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei, China
⁹¹ Institute of Frontier and Interdisciplinary Science and Key Laboratory of Particle Physics and Particle Irradiation (MOE), Shandong University, Qingdao, China
⁹² School of Physics and Astronomy, Shanghai Jiao Tong University, Key Laboratory for Particle Astrophysics and Cosmology (MOE), SKLPPC, Shanghai, China
⁹³ Tsung-Dao Lee Institute, Shanghai, China
⁹⁴ School of Physics, Zhengzhou University, China
⁹⁵ Kirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
⁹⁶ Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
⁹⁷ Department of Physics, Chinese University of Hong Kong, Shatin, N.T., Hong Kong
⁹⁸ Department of Physics, University of Hong Kong, Hong Kong, China
⁹⁹ Department of Physics and Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
¹⁰⁰ Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
¹⁰¹ IJCLab, Université Paris-Saclay, CNRS/IN2P3, 91405, Orsay, France
¹⁰² Centro Nacional de Microelectrónica (IMB-CNM-CSIC), Barcelona, Spain
¹⁰³ Department of Physics, Indiana University, Bloomington, IN, USA
¹⁰⁴ INFN Gruppo Collegato di Udine, Sezione di Trieste, Udine, Italy
¹⁰⁵ ICTP, Trieste, Italy
¹⁰⁶ Dipartimento Politecnico di Ingegneria e Architettura, Università di Udine, Udine, Italy
¹⁰⁷ INFN Sezione di Lecce, Lecce, Italy
¹⁰⁸ Dipartimento di Matematica e Fisica, Università del Salento, Lecce, Italy
¹⁰⁹ INFN Sezione di Milano, Milan, Italy
¹¹⁰ Dipartimento di Fisica, Università di Milano, Milan, Italy
¹¹¹ INFN Sezione di Napoli, Naples, Italy
¹¹² Dipartimento di Fisica, Università di Napoli, Naples, Italy
¹¹³ INFN Sezione di Pavia, Pavia, Italy
¹¹⁴ Dipartimento di Fisica, Università di Pavia, Pavia, Italy
¹¹⁵ INFN Sezione di Pisa, Pisa, Italy
¹¹⁶ Dipartimento di Fisica E. Fermi, Università di Pisa, Pisa, Italy
¹¹⁷ INFN Sezione di Roma, Rome, Italy
¹¹⁸ Dipartimento di Fisica, Sapienza Università di Roma, Rome, Italy
¹¹⁹ INFN Sezione di Roma Tor Vergata, Rome, Italy
¹²⁰ Dipartimento di Fisica, Università di Roma Tor Vergata, Rome, Italy
¹²¹ INFN Sezione di Roma Tre, Rome, Italy
¹²² Dipartimento di Matematica e Fisica, Università Roma Tre, Rome, Italy
¹²³ INFN-TIFPA, Rome, Italy
¹²⁴ Università degli Studi di Trento, Trento, Italy
¹²⁵ Universität Innsbruck, Department of Astro and Particle Physics, Innsbruck, Austria
¹²⁶ University of Iowa, Iowa City, IA, USA
¹²⁷ Department of Physics and Astronomy, Iowa State University, Ames, IA, USA
¹²⁸ Istinye University, Sariyer, Istanbul, Turkey
¹²⁹ Departamento de Engenharia Elétrica, Universidade Federal de Juiz de Fora (UFJF), Juiz de Fora, Brazil
¹³⁰ Universidade Federal do Rio De Janeiro COPPE/EE/IF, Rio de Janeiro, Brazil
¹³¹ Instituto de Física, Universidade de São Paulo, São Paulo, Brazil
¹³² Rio de Janeiro State University, Rio de Janeiro, Brazil
¹³³ Federal University of Bahia, Bahia, Brazil
¹³⁴ KEK, High Energy Accelerator Research Organization, Tsukuba, Japan
¹³⁵ Graduate School of Science, Kobe University, Kobe, Japan
¹³⁶ AGH University of Krakow, Faculty of Physics and Applied Computer Science, Krakow, Poland
¹³⁷ Marian Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland
¹³⁸ Institute of Nuclear Physics Polish Academy of Sciences, Krakow, Poland
¹³⁹ Faculty of Science, Kyoto University, Kyoto, Japan
¹⁴⁰ Research Center for Advanced Particle Physics and Department of Physics, Kyushu University, Fukuoka, Japan
¹⁴¹ L2IT, Université de Toulouse, CNRS/IN2P3, UPS, Toulouse, France
¹⁴² Instituto de Física La Plata, Universidad Nacional de La Plata and CONICET, La Plata, Argentina
¹⁴³ Physics Department, Lancaster University, Lancaster, UK
¹⁴⁴ Oliver Lodge Laboratory, University of Liverpool, Liverpool, UK
¹⁴⁵ Department of Experimental Particle Physics, Jožef Stefan Institute and Department of Physics, University of Ljubljana, Ljubljana, Slovenia
¹⁴⁶ School of Physics and Astronomy, Queen Mary University of London, London, UK
¹⁴⁷ Department of Physics, Royal Holloway University of London, Egham, UK
¹⁴⁸ Department of Physics and Astronomy, University College London, London, UK
¹⁴⁹ Louisiana Tech University, Ruston, LA, USA
¹⁵⁰ Fysiska institutionen, Lunds universitet, Lund, Sweden
¹⁵¹ Departamento de Física Teorica C-15 and CIAFF, Universidad Autónoma de Madrid, Madrid, Spain
¹⁵² Institut für Physik, Universität Mainz, Mainz, Germany
¹⁵³ School of Physics and Astronomy, University of Manchester, Manchester, UK
¹⁵⁴ CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France
¹⁵⁵ Department of Physics, University of Massachusetts, Amherst, MA, USA
¹⁵⁶ Department of Physics, McGill University, Montreal, QC, Canada
¹⁵⁷ School of Physics, University of Melbourne, Victoria, Australia
¹⁵⁸ Department of Physics, University of Michigan, Ann Arbor, MI, USA
¹⁵⁹ Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA
¹⁶⁰ Group of Particle Physics, University of Montreal, Montreal, QC, Canada
¹⁶¹ Fakultät für Physik, Ludwig-Maximilians-Universität München, München, Germany
¹⁶² Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), München, Germany
¹⁶³ Graduate School of Science and Kobayashi-Maskawa Institute, Nagoya University, Nagoya, Japan
¹⁶⁴ Department of Physics, Nanjing University, Nanjing, China
¹⁶⁵ School of Science, Shenzhen Campus of Sun Yat-sen University, Shenzhen, China
¹⁶⁶ University of Chinese Academy of Science (UCAS), Beijing, China
¹⁶⁷ Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM, USA
¹⁶⁸ Institute for Mathematics, Astrophysics and Particle Physics, Radboud University/Nikhef, Nijmegen, The Netherlands
¹⁶⁹ Nikhef National Institute for Subatomic Physics and University of Amsterdam, Amsterdam, The Netherlands
¹⁷⁰ Department of Physics, Northern Illinois University, DeKalb, IL, USA
¹⁷¹ New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
¹⁷² United Arab Emirates University, Al Ain, United Arab Emirates
¹⁷³ Department of Physics, New York University, New York, NY, USA
¹⁷⁴ Ochanomizu University, Otsuka, Bunkyo-ku, Tokyo, Japan
¹⁷⁵ Ohio State University, Columbus, OH, USA
¹⁷⁶ Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK, USA
¹⁷⁷ Department of Physics, Oklahoma State University, Stillwater, OK, USA
¹⁷⁸ Palacký University, Joint Laboratory of Optics, Olomouc, Czech Republic
¹⁷⁹ Institute for Fundamental Science, University of Oregon, Eugene, OR, USA
¹⁸⁰ Graduate School of Science, Osaka University, Osaka, Japan
¹⁸¹ Department of Physics, University of Oslo, Oslo, Norway
¹⁸² Department of Physics, Oxford University, Oxford, UK
¹⁸³ LPNHE, Sorbonne Université, Université Paris Cité, CNRS/IN2P3, Paris, France
¹⁸⁴ Department of Physics, University of Pennsylvania, Philadelphia, PA, USA
¹⁸⁵ Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, USA
¹⁸⁶ Laboratório de Instrumentação e Física Experimental de Partículas - LIP, Lisbon, Portugal
¹⁸⁷ Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
¹⁸⁸ Departamento de Física, Universidade de Coimbra, Coimbra, Portugal
¹⁸⁹ Centro de Física Nuclear da Universidade de Lisboa, Lisbon, Portugal
¹⁹⁰ Departamento de Física, Universidade do Minho, Braga, Portugal
¹⁹¹ Departamento de Física Teórica y del Cosmos, Universidad de Granada, Granada, Spain
¹⁹² Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
¹⁹³ Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic
¹⁹⁴ Czech Technical University in Prague, Prague, Czech Republic
¹⁹⁵ Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic
¹⁹⁶ Particle Physics Department, Rutherford Appleton Laboratory, Didcot, UK
¹⁹⁷ IRFU, CEA, Université Paris-Saclay, Gif-sur-Yvette, France
¹⁹⁸ Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz, CA, USA
¹⁹⁹ Departamento de Física, Pontificia Universidad Católica de Chile, Santiago, Chile
²⁰⁰ Millennium Institute for Subatomic physics at high energy frontier (SAPHIR), Santiago, Chile
²⁰¹ Instituto de Investigación Multidisciplinario en Ciencia y Tecnología y Departamento de Física, Universidad de La Serena, La Serena, Chile
²⁰² Universidad Andres Bello, Department of Physics, Santiago, Chile
²⁰³ Instituto de Alta Investigación, Universidad de Tarapacá, Arica, Chile
²⁰⁴ Departamento de Física, Universidad Técnica Federico Santa María, Valparaíso, Chile
²⁰⁵ Department of Physics, Institute of Science, Tokyo, Japan
²⁰⁶ Department of Physics, University of Washington, Seattle, WA, USA
²⁰⁷ Department of Physics and Astronomy, University of Sheffield, Sheffield, UK
²⁰⁸ Department of Physics, Shinshu University, Nagano, Japan
²⁰⁹ Department Physik, Universität Siegen, Siegen, Germany
²¹⁰ Department of Physics, Simon Fraser University, Burnaby, BC, Canada
²¹¹ SLAC National Accelerator Laboratory, Stanford, CA, USA
²¹² Department of Physics, Royal Institute of Technology, Stockholm, Sweden
²¹³ Departments of Physics and Astronomy, Stony Brook University, Stony Brook, NY, USA
²¹⁴ Department of Physics and Astronomy, University of Sussex, Brighton, UK
²¹⁵ School of Physics, University of Sydney, Sydney, Australia
²¹⁶ Institute of Physics, Academia Sinica, Taipei, Taiwan
²¹⁷ E. Andronikashvili Institute of Physics, Iv. Javakhishvili Tbilisi State University, Tbilisi, Georgia
²¹⁸ High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia
²¹⁹ University of Georgia, Tbilisi, Georgia
²²⁰ Department of Physics, Technion, Israel Institute of Technology, Haifa, Israel
²²¹ Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel
²²² Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece
²²³ International Center for Elementary Particle Physics and Department of Physics, University of Tokyo, Tokyo, Japan
²²⁴ Department of Physics, University of Toronto, Toronto, ON, Canada
²²⁵ TRIUMF, Vancouver, BC, Canada
²²⁶ Department of Physics and Astronomy, York University, Toronto, ON, Canada
²²⁷ Division of Physics and Tomonaga Center for the History of the Universe, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Japan
²²⁸ Department of Physics and Astronomy, Tufts University, Medford, MA, USA
²²⁹ Department of Physics and Astronomy, University of California Irvine, Irvine, CA, USA
²³⁰ University of Sharjah, Sharjah, United Arab Emirates
²³¹ Department of Physics and Astronomy, University of Uppsala, Uppsala, Sweden
²³² Department of Physics, University of Illinois, Urbana, IL, USA
²³³ Instituto de Física Corpuscular (IFIC), Centro Mixto Universidad de Valencia - CSIC, Valencia, Spain
²³⁴ Department of Physics, University of British Columbia, Vancouver, BC, Canada
²³⁵ Department of Physics and Astronomy, University of Victoria, Victoria, BC, Canada
²³⁶ Fakultät für Physik und Astronomie, Julius-Maximilians-Universität Würzburg, Würzburg, Germany
²³⁷ Department of Physics, University of Warwick, Coventry, UK
²³⁸ Waseda University, Tokyo, Japan
²³⁹ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot, Israel
²⁴⁰ Department of Physics, University of Wisconsin, Madison, WI, USA
²⁴¹ Fakultät für Mathematik und Naturwissenschaften, Fachgruppe Physik, Bergische Universität Wuppertal, Wuppertal, Germany
²⁴² Department of Physics, Yale University, New Haven, CT, USA
²⁴³ Also Affiliated with an Institute Covered by a Cooperation Agreement with CERN, Geneva, Switzerland
²⁴⁴ An-Najah National University, Nablus, Palestine
²⁴⁵ Borough of Manhattan Community College, City University of New York, New York, NY, USA
²⁴⁶ Center for Interdisciplinary Research and Innovation (CIRI-AUTH), Thessaloniki, Greece
²⁴⁷ CERN, Geneva, Switzerland
²⁴⁸ CMD-AC UNEC Research Center, Azerbaijan State University of Economics (UNEC), Azerbaijan
²⁴⁹ Département de Physique Nucléaire et Corpusculaire, Université de Genève, Genève, Switzerland
²⁵⁰ Departament de Fisica de la Universitat Autonoma de Barcelona, Barcelona, Spain
²⁵¹ Department of Financial and Management Engineering, University of the Aegean, Chios, Greece
²⁵² Department of Physics, California State University, Sacramento, USA
²⁵³ Department of Physics, King’s College London, London, UK
²⁵⁴ Department of Physics, Stanford University, Stanford, CA, USA
²⁵⁵ Department of Physics, Stellenbosch University, South Africa
²⁵⁶ Department of Physics, University of Fribourg, Fribourg, Switzerland
²⁵⁷ Department of Physics, University of Thessaly, Greece
²⁵⁸ Department of Physics, Westmont College, Santa Barbara, USA
²⁵⁹ Faculty of Physics, Sofia University, ’St. Kliment Ohridski’, Sofia, Bulgaria
²⁶⁰ Hellenic Open University, Patras, Greece
²⁶¹ Imam Mohammad Ibn Saud Islamic University, Riyadh, Saudi Arabia
²⁶² Institucio Catalana de Recerca i Estudis Avancats, ICREA, Barcelona, Spain
²⁶³ Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany
²⁶⁴ Institute for Nuclear Research and Nuclear Energy (INRNE) of the Bulgarian Academy of Sciences, Sofia, Bulgaria
²⁶⁵ Institute of Applied Physics, Mohammed VI Polytechnic University, Ben Guerir, Morocco
²⁶⁶ Institute of Particle Physics (IPP), Ottawa, Canada
²⁶⁷ Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan
²⁶⁸ Institute of Theoretical Physics, Ilia State University, Tbilisi, Georgia
²⁶⁹ National Institute of Physics, University of the Philippines Diliman (Philippines), Philippines
²⁷⁰ Technical University of Munich, Munich, Germany
²⁷¹ The Collaborative Innovation Center of Quantum Matter (CICQM), Beijing, China
²⁷² TRIUMF, Vancouver, BC, Canada
²⁷³ Università di Napoli Parthenope, Naples, Italy
²⁷⁴ University of Colorado Boulder, Department of Physics, Colorado, USA
²⁷⁵ Washington College, Chestertown, MD, USA
²⁷⁶ Yeditepe University, Physics Department, Istanbul, Turkey
²⁷⁷ CERN, 1211, Geneva 23, Switzerland

^a atlas.publications@cern.ch

Received: 16 July 2024
Accepted: 17 December 2024
Published online: 6 February 2025

Abstract

A search for a light charged Higgs boson produced in decays of the top quark, $t\to H^{\pm }b$ with $H^{\pm }\to cs$, is presented. This search targets the production of top-quark pairs $t\overline{t}\to Wb{H}^{\pm }b$, with $W\to \ell \nu$ ($\ell =e,\mu$), resulting in a lepton-plus-jets final state characterised by an isolated electron or muon and at least four jets. The search exploits b-quark and c-quark identification techniques as well as multivariate methods to suppress the dominant $t\overline{t}$ background. The data analysed correspond to $140{\text{fb}}^{-1}$ of $\mathit{pp}$ collisions at $\sqrt{s}=13\text{TeV}$ recorded with the ATLAS detector at the LHC between 2015 and 2018. Observed (expected) 95% confidence-level upper limits on the branching fraction $\mathcal{B}(t\to H^{\pm }b)$, assuming $\mathcal{B}(t\to Wb)+\mathcal{B}(t\to H^{\pm }(\to cs)b)=1.0$, are set between 0.066% (0.077%) and 3.6% (2.3%) for a charged Higgs boson with a mass between 60 and 168 GeV.