https://doi.org/10.1140/epjc/s10052-020-7997-4
Regular Article - Experimental Physics
Search for light long-lived neutral particles produced in pp collisions at 
and decaying into collimated leptons or light hadrons with the ATLAS detector
1
Department of Physics, University of Adelaide, Adelaide, Australia
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Physics Department, SUNY Albany, Albany, NY, USA
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Department of Physics, University of Alberta, Edmonton, AB, Canada
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Department of Physics, Ankara University, Ankara, Turkey
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Istanbul Aydin University, Istanbul, Turkey
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Division of Physics, TOBB University of Economics and Technology, Ankara, Turkey
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LAPP, Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS/IN2P3, Annecy, France
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High Energy Physics Division, Argonne National Laboratory, Argonne, IL, USA
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Department of Physics, University of Arizona, Tucson, AZ, USA
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Department of Physics, University of Texas at Arlington, Arlington, TX, USA
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Physics Department, National and Kapodistrian University of Athens, Athens, Greece
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Physics Department, National Technical University of Athens, Zografou, Greece
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Department of Physics, University of Texas at Austin, Austin, TX, USA
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Bahcesehir University, Faculty of Engineering and Natural Sciences, Istanbul, Turkey
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Istanbul Bilgi University, Faculty of Engineering and Natural Sciences, Istanbul, Turkey
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Department of Physics, Bogazici University, Istanbul, Turkey
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Department of Physics Engineering, Gaziantep University, Gaziantep, Turkey
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Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan
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Institut de Física d’Altes Energies (IFAE), Barcelona Institute of Science and Technology, Barcelona, Spain
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Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
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Physics Department, Tsinghua University, Beijing, China
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Department of Physics, Nanjing University, Nanjing, China
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University of Chinese Academy of Science (UCAS), Beijing, China
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Institute of Physics, University of Belgrade, Belgrade, Serbia
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Department for Physics and Technology, University of Bergen, Bergen, Norway
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Physics Division, Lawrence Berkeley National Laboratory and University of California, Berkeley, CA, USA
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Institut für Physik, Humboldt Universität zu Berlin, Berlin, Germany
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Albert Einstein Center for Fundamental Physics and Laboratory for High Energy Physics, University of Bern, Bern, Switzerland
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School of Physics and Astronomy, University of Birmingham, Birmingham, UK
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Facultad de Ciencias y Centro de Investigaciónes, Universidad Antonio Nariño, Bogotá, Colombia
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Departamento de Física, Universidad Nacional de Colombia, Bogotá, Colombia
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Dipartimento di Fisica, INFN Bologna and Universita’ di Bologna, Bologna, Italy
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INFN Sezione di Bologna, Bologna, Italy
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Physikalisches Institut, Universität Bonn, Bonn, Germany
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Department of Physics, Boston University, Boston, MA, USA
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Department of Physics, Brandeis University, Waltham, MA, USA
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Transilvania University of Brasov, Brasov, Romania
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Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania
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Department of Physics, Alexandru Ioan Cuza University of Iasi, Iasi, Romania
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National Institute for Research and Development of Isotopic and Molecular Technologies, Physics Department, Cluj-Napoca, Romania
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University Politehnica Bucharest, Bucharest, Romania
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West University in Timisoara, Timisoara, Romania
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Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
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Department of Subnuclear Physics, Institute of Experimental Physics of the Slovak Academy of Sciences, Kosice, Slovak Republic
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Physics Department, Brookhaven National Laboratory, Upton, NY, USA
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Departamento de Física, Universidad de Buenos Aires, Buenos Aires, Argentina
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California State University, Long Beach, CA, USA
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Cavendish Laboratory, University of Cambridge, Cambridge, UK
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Department of Physics, University of Cape Town, Cape Town, South Africa
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iThemba Labs, Western Cape, South Africa
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Department of Mechanical Engineering Science, University of Johannesburg, Johannesburg, South Africa
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University of South Africa, Department of Physics, Pretoria, South Africa
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School of Physics, University of the Witwatersrand, Johannesburg, South Africa
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Department of Physics, Carleton University, Ottawa, ON, Canada
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Faculté des Sciences Ain Chock, Réseau Universitaire de Physique des Hautes Energies, Université Hassan II, Casablanca, Morocco
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Faculté des Sciences, Université Ibn-Tofail, Kénitra, Morocco
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Faculté des Sciences Semlalia, Université Cadi Ayyad, LPHEA-Marrakech, Marrakesh, Morocco
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Faculté des Sciences, Université Mohamed Premier and LPTPM, Oujda, Morocco
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Faculté des sciences, Université Mohammed V, Rabat, Morocco
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CERN, Geneva, Switzerland
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Enrico Fermi Institute, University of Chicago, Chicago, IL, USA
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LPC, Université Clermont Auvergne, CNRS/IN2P3, Clermont-Ferrand, France
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Nevis Laboratory, Columbia University, Irvington, NY, USA
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Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
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Dipartimento di Fisica, Università della Calabria, Rende, Italy
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INFN Gruppo Collegato di Cosenza, Laboratori Nazionali di Frascati, Frascati, Italy
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Physics Department, Southern Methodist University, Dallas, TX, USA
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Physics Department, University of Texas at Dallas, Richardson, TX, USA
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National Centre for Scientific Research “Demokritos”, Agia Paraskevi, Greece
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Department of Physics, Stockholm University, Stockholm, Sweden
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Oskar Klein Centre, Stockholm, Sweden
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Deutsches Elektronen-Synchrotron DESY, Hamburg and Zeuthen, Germany
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Lehrstuhl für Experimentelle Physik IV, Technische Universität Dortmund, Dortmund, Germany
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Institut für Kern- und Teilchenphysik, Technische Universität Dresden, Dresden, Germany
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Department of Physics, Duke University, Durham, NC, USA
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SUPA-School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK
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INFN e Laboratori Nazionali di Frascati, Frascati, Italy
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Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
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II. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen, Germany
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Département de Physique Nucléaire et Corpusculaire, Université de Genève, Geneva, Switzerland
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Dipartimento di Fisica, Università di Genova, Genoa, Italy
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INFN Sezione di Genova, Genoa, Italy
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II. Physikalisches Institut, Justus-Liebig-Universität Giessen, Giessen, Germany
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SUPA-School of Physics and Astronomy, University of Glasgow, Glasgow, UK
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LPSC, Université Grenoble Alpes, CNRS/IN2P3, Grenoble INP, Grenoble, France
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Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge, MA, USA
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Department of Modern Physics and State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei, China
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Institute of Frontier and Interdisciplinary Science and Key Laboratory of Particle Physics and Particle Irradiation (MOE), Shandong University, Qingdao, China
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School of Physics and Astronomy, Shanghai Jiao Tong University, KLPPAC-MoE, SKLPPC, Shanghai, China
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Tsung-Dao Lee Institute, Shanghai, China
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Kirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
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Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
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Faculty of Applied Information Science, Hiroshima Institute of Technology, Hiroshima, Japan
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Department of Physics, Chinese University of Hong Kong, Shatin, N.T., Hong Kong
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Department of Physics, University of Hong Kong, Pok Fu Lam, Hong Kong
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Department of Physics and Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
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Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
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IJCLab, Université Paris-Saclay, CNRS/IN2P3, 91405, Orsay, France
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Department of Physics, Indiana University, Bloomington, IN, USA
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INFN Gruppo Collegato di Udine, Sezione di Trieste, Udine, Italy
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ICTP, Trieste, Italy
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Dipartimento Politecnico di Ingegneria e Architettura, Università di Udine, Udine, Italy
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INFN Sezione di Lecce, Lecce, Italy
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Dipartimento di Matematica e Fisica, Università del Salento, Lecce, Italy
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INFN Sezione di Milano, Milan, Italy
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Dipartimento di Fisica, Università di Milano, Milan, Italy
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INFN Sezione di Napoli, Naples, Italy
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Dipartimento di Fisica, Università di Napoli, Naples, Italy
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INFN Sezione di Pavia, Pavia, Italy
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Dipartimento di Fisica, Università di Pavia, Pavia, Italy
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INFN Sezione di Pisa, Pisa, Italy
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Dipartimento di Fisica E. Fermi, Università di Pisa, Pisa, Italy
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INFN Sezione di Roma, Rome, Italy
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Dipartimento di Fisica, Sapienza Università di Roma, Rome, Italy
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INFN Sezione di Roma Tor Vergata, Rome, Italy
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Dipartimento di Fisica, Università di Roma Tor Vergata, Rome, Italy
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INFN Sezione di Roma Tre, Rome, Italy
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Dipartimento di Matematica e Fisica, Università Roma Tre, Rome, Italy
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INFN-TIFPA, Povo, Italy
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Università degli Studi di Trento, Trento, Italy
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Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität, Innsbruck, Austria
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University of Iowa, Iowa City, IA, USA
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Department of Physics and Astronomy, Iowa State University, Ames, IA, USA
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Joint Institute for Nuclear Research, Dubna, Russia
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Departamento de Engenharia Elétrica, Universidade Federal de Juiz de Fora (UFJF), Juiz de Fora, Brazil
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Universidade Federal do Rio De Janeiro COPPE/EE/IF, Rio de Janeiro, Brazil
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Universidade Federal de São João del Rei (UFSJ), São João del Rei, Brazil
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Instituto de Física, Universidade de São Paulo, São Paulo, Brazil
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KEK, High Energy Accelerator Research Organization, Tsukuba, Japan
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Graduate School of Science, Kobe University, Kobe, Japan
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AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Kraków, Poland
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Marian Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
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Institute of Nuclear Physics Polish Academy of Sciences, Kraków, Poland
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Faculty of Science, Kyoto University, Kyoto, Japan
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Kyoto University of Education, Kyoto, Japan
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Research Center for Advanced Particle Physics and Department of Physics, Kyushu University, Fukuoka, Japan
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Instituto de Física La Plata, Universidad Nacional de La Plata and CONICET, La Plata, Argentina
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Physics Department, Lancaster University, Lancaster, UK
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Oliver Lodge Laboratory, University of Liverpool, Liverpool, UK
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Department of Experimental Particle Physics, Jožef Stefan Institute and Department of Physics, University of Ljubljana, Ljubljana, Slovenia
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School of Physics and Astronomy, Queen Mary University of London, London, UK
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Department of Physics, Royal Holloway University of London, Egham, UK
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Department of Physics and Astronomy, University College London, London, UK
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Louisiana Tech University, Ruston, LA, USA
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Fysiska institutionen, Lunds universitet, Lund, Sweden
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Centre de Calcul de l’Institut National de Physique Nucléaire et de Physique des Particules (IN2P3), Villeurbanne, France
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Departamento de Física Teorica C-15 and CIAFF, Universidad Autónoma de Madrid, Madrid, Spain
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Institut für Physik, Universität Mainz, Mainz, Germany
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School of Physics and Astronomy, University of Manchester, Manchester, UK
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CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France
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Department of Physics, University of Massachusetts, Amherst, MA, USA
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Department of Physics, McGill University, Montreal, QC, Canada
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School of Physics, University of Melbourne, Melbourne, VIC, Australia
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Department of Physics, University of Michigan, Ann Arbor, MI, USA
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Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA
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B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk, Belarus
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Research Institute for Nuclear Problems of Byelorussian State University, Minsk, Belarus
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Group of Particle Physics, University of Montreal, Montreal, QC, Canada
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P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia
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National Research Nuclear University MEPhI, Moscow, Russia
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D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow, Russia
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Fakultät für Physik, Ludwig-Maximilians-Universität München, Munich, Germany
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Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Munich, Germany
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Nagasaki Institute of Applied Science, Nagasaki, Japan
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Graduate School of Science and Kobayashi-Maskawa Institute, Nagoya University, Nagoya, Japan
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Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM, USA
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Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen, The Netherlands
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Nikhef National Institute for Subatomic Physics and University of Amsterdam, Amsterdam, The Netherlands
169
Department of Physics, Northern Illinois University, DeKalb, IL, USA
170
Budker Institute of Nuclear Physics and NSU, SB RAS, Novosibirsk, Russia
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Novosibirsk State University, Novosibirsk, Russia
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Institute for High Energy Physics of the National Research Centre Kurchatov Institute, Protvino, Russia
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Institute for Theoretical and Experimental Physics named by A.I. Alikhanov of National Research Centre “Kurchatov Institute”, Moscow, Russia
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Department of Physics, New York University, New York, NY, USA
175
Ochanomizu University, Otsuka, Bunkyo-ku, Tokyo, Japan
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Ohio State University, Columbus, OH, USA
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Faculty of Science, Okayama University, Okayama, Japan
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Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK, USA
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Department of Physics, Oklahoma State University, Stillwater, OK, USA
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Palacký University, RCPTM, Joint Laboratory of Optics, Olomouc, Czech Republic
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Center for High Energy Physics, University of Oregon, Eugene, OR, USA
182
Graduate School of Science, Osaka University, Osaka, Japan
183
Department of Physics, University of Oslo, Oslo, Norway
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Department of Physics, Oxford University, Oxford, UK
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LPNHE, Sorbonne Université, Université de Paris, CNRS/IN2P3, Paris, France
186
Department of Physics, University of Pennsylvania, Philadelphia, PA, USA
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Konstantinov Nuclear Physics Institute of National Research Centre “Kurchatov Institute”, PNPI, St. Petersburg, Russia
188
Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, USA
189
Laboratório de Instrumentação e Física Experimental de Partículas - LIP, Lisbon, Portugal
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Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
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Departamento de Física, Universidade de Coimbra, Coimbra, Portugal
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Centro de Física Nuclear da Universidade de Lisboa, Lisbon, Portugal
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Departamento de Física, Universidade do Minho, Braga, Portugal
194
Departamento de Física Teórica y del Cosmos, Universidad de Granada, Granada, Spain
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Dep Física and CEFITEC of Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
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Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal
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Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic
198
Czech Technical University in Prague, Prague, Czech Republic
199
Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic
200
Particle Physics Department, Rutherford Appleton Laboratory, Didcot, UK
201
IRFU, CEA, Université Paris-Saclay, Gif-sur-Yvette, France
202
Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz, CA, USA
203
Departamento de Física, Pontificia Universidad Católica de Chile, Santiago, Chile
204
Universidad Andres Bello, Department of Physics, Santiago, Chile
205
Instituto de Alta Investigación, Universidad de Tarapacá, Arica, Chile
206
Departamento de Física, Universidad Técnica Federico Santa María, Valparaíso, Chile
207
Department of Physics, University of Washington, Seattle, WA, USA
208
Department of Physics and Astronomy, University of Sheffield, Sheffield, UK
209
Department of Physics, Shinshu University, Nagano, Japan
210
Department Physik, Universität Siegen, Siegen, Germany
211
Department of Physics, Simon Fraser University, Burnaby, BC, Canada
212
SLAC National Accelerator Laboratory, Stanford, CA, USA
213
Physics Department, Royal Institute of Technology, Stockholm, Sweden
214
Departments of Physics and Astronomy, Stony Brook University, Stony Brook, NY, USA
215
Department of Physics and Astronomy, University of Sussex, Brighton, UK
216
School of Physics, University of Sydney, Sydney, Australia
217
Institute of Physics, Academia Sinica, Taipei, Taiwan
218
E. Andronikashvili Institute of Physics, Iv. Javakhishvili Tbilisi State University, Tbilisi, Georgia
219
High Energy Physics Institute, Tbilisi State University, 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
Graduate School of Science and Technology, Tokyo Metropolitan University, Tokyo, Japan
225
Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
226
Tomsk State University, Tomsk, Russia
227
Department of Physics, University of Toronto, Toronto, ON, Canada
228
TRIUMF, Vancouver, BC, Canada
229
Department of Physics and Astronomy, York University, Toronto, ON, Canada
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Division of Physics and Tomonaga Center for the History of the Universe, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Japan
231
Department of Physics and Astronomy, Tufts University, Medford, MA, USA
232
Department of Physics and Astronomy, University of California Irvine, Irvine, CA, USA
233
Department of Physics and Astronomy, University of Uppsala, Uppsala, Sweden
234
Department of Physics, University of Illinois, Urbana, IL, USA
235
Instituto de Física Corpuscular (IFIC), Centro Mixto Universidad de Valencia-CSIC, Valencia, Spain
236
Department of Physics, University of British Columbia, Vancouver, BC, Canada
237
Department of Physics and Astronomy, University of Victoria, Victoria, BC, Canada
238
Fakultät für Physik und Astronomie, Julius-Maximilians-Universität Würzburg, Würzburg, Germany
239
Department of Physics, University of Warwick, Coventry, UK
240
Waseda University, Tokyo, Japan
241
Department of Particle Physics, Weizmann Institute of Science, Rehovot, Israel
242
Department of Physics, University of Wisconsin, Madison, WI, USA
243
Fakultät für Mathematik und Naturwissenschaften, Fachgruppe Physik, Bergische Universität Wuppertal, Wuppertal, Germany
244
Department of Physics, Yale University, New Haven, CT, USA
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Yerevan Physics Institute, Yerevan, Armenia
* e-mail: atlas.publications@cern.ch
Received:
4
September
2019
Accepted:
4
May
2020
Published online:
20
May
2020
Several models of physics beyond the Standard Model predict the existence of dark photons, light neutral particles decaying into collimated leptons or light hadrons. This paper presents a search for long-lived dark photons produced from the decay of a Higgs boson or a heavy scalar boson and decaying into displaced collimated Standard Model fermions. The search uses data corresponding to an integrated luminosity of 36.1 fb
collected in proton–proton collisions at 
recorded in 2015–2016 with the ATLAS detector at the Large Hadron Collider. The observed number of events is consistent with the expected background, and limits on the production cross section times branching fraction as a function of the proper decay length of the dark photon are reported. A cross section times branching fraction above 4 pb is excluded for a Higgs boson decaying into two dark photons for dark-photon decay lengths between 1.5 mm and 307 mm.
© CERN for the benefit of the ATLAS collaboration, 2020
