Eur. Phys. J. C (2025) 85: 553
https://doi.org/10.1140/epjc/s10052-025-13971-y

Regular Article - Experimental Physics

Measurement of the inclusive isolated-photon production cross section in pp and Pb–Pb collisions at $\sqrt{{\mathit{s}}_{\mathbf{NN}}}=\mathbf{5.02}$ TeV

¹ A.I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation, Yerevan, Armenia
² AGH University of Krakow, Cracow, Poland
³ Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, Kiev, Ukraine
⁴ Bose Institute, Department of Physics and Centre for Astroparticle Physics and Space Science (CAPSS), Kolkata, India
⁵ California Polytechnic State University, San Luis Obispo, CA, USA
⁶ Central China Normal University, Wuhan, China
⁷ Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), Havana, Cuba
⁸ Centro de Investigación y de Estudios Avanzados (CINVESTAV), Mexico City and Mérida, Mexico
⁹ Chicago State University, Chicago, IL, USA
¹⁰ China Institute of Atomic Energy, Beijing, China
¹¹ China University of Geosciences, Wuhan, China
¹² Chungbuk National University, Cheongju, Republic of Korea
¹³ Comenius University Bratislava, Faculty of Mathematics, Physics and Informatics, Bratislava, Slovak Republic
¹⁴ Creighton University, Omaha, NE, USA
¹⁵ Department of Physics, Aligarh Muslim University, Aligarh, India
¹⁶ Department of Physics, Pusan National University, Pusan, Republic of Korea
¹⁷ Department of Physics, Sejong University, Seoul, Republic of Korea
¹⁸ Department of Physics, University of California, Berkeley, CA, USA
¹⁹ Department of Physics, University of Oslo, Oslo, Norway
²⁰ Department of Physics and Technology, University of Bergen, Bergen, Norway
²¹ Dipartimento di Fisica, Università di Pavia, Pavia, Italy
²² Dipartimento di Fisica dell’Università and Sezione INFN, Cagliari, Italy
²³ Dipartimento di Fisica dell’Università and Sezione INFN, Trieste, Italy
²⁴ Dipartimento di Fisica dell’Università and Sezione INFN, Turin, Italy
²⁵ Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Bologna, Italy
²⁶ Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Catania, Italy
²⁷ Dipartimento di Fisica e Astronomia dell’Università and Sezione INFN, Padua, Italy
²⁸ Dipartimento di Fisica ‘E.R. Caianiello’ dell’Università and Gruppo Collegato INFN, Salerno, Italy
²⁹ Dipartimento DISAT del Politecnico and Sezione INFN, Turin, Italy
³⁰ Dipartimento di Scienze MIFT, Università di Messina, Messina, Italy
³¹ Dipartimento Interateneo di Fisica ‘M. Merlin’ and Sezione INFN, Bari, Italy
³² European Organization for Nuclear Research (CERN), Geneva, Switzerland
³³ Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, University of Split, Split, Croatia
³⁴ Faculty of Engineering and Science, Western Norway University of Applied Sciences, Bergen, Norway
³⁵ Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic
³⁶ Faculty of Physics, Sofia University, Sofia, Bulgaria
³⁷ Faculty of Science, P.J. Šafárik University, Košice, Slovak Republic
³⁸ Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany
³⁹ Fudan University, Shanghai, China
⁴⁰ Gangneung-Wonju National University, Gangneung, Republic of Korea
⁴¹ Department of Physics, Gauhati University, Guwahati, India
⁴² Helmholtz-Institut für Strahlen- und Kernphysik, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
⁴³ Helsinki Institute of Physics (HIP), Helsinki, Finland
⁴⁴ High Energy Physics Group, Universidad Autónoma de Puebla, Puebla, Mexico
⁴⁵ Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania
⁴⁶ HUN-REN Wigner Research Centre for Physics, Budapest, Hungary
⁴⁷ Indian Institute of Technology Bombay (IIT), Mumbai, India
⁴⁸ Indian Institute of Technology Indore, Indore, India
⁴⁹ INFN, Laboratori Nazionali di Frascati, Frascati, Italy
⁵⁰ INFN, Sezione di Bari, Bari, Italy
⁵¹ INFN, Sezione di Bologna, Bologna, Italy
⁵² INFN, Sezione di Cagliari, Cagliari, Italy
⁵³ INFN, Sezione di Catania, Catania, Italy
⁵⁴ INFN, Sezione di Padova, Padova, Italy
⁵⁵ INFN, Sezione di Pavia, Pavia, Italy
⁵⁶ INFN, Sezione di Torino, Turin, Italy
⁵⁷ INFN, Sezione di Trieste, Trieste, Italy
⁵⁸ Inha University, Incheon, Republic of Korea
⁵⁹ Institute for Gravitational and Subatomic Physics (GRASP), Utrecht University/Nikhef, Utrecht, The Netherlands
⁶⁰ Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovak Republic
⁶¹ Institute of Physics, Homi Bhabha National Institute, Bhubaneswar, India
⁶² Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic
⁶³ Institute of Space Science (ISS), Bucharest, Romania
⁶⁴ Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt, Germany
⁶⁵ Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico City, Mexico
⁶⁶ Instituto de Física, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil
⁶⁷ Instituto de Física, Universidad Nacional Autónoma de México, Mexico City, Mexico
⁶⁸ iThemba LABS, National Research Foundation, Somerset West, South Africa
⁶⁹ Jeonbuk National University, Jeonju, Republic of Korea
⁷⁰ Johann-Wolfgang-Goethe Universität Frankfurt Institut für Informatik, Fachbereich Informatik und Mathematik, Frankfurt, Germany
⁷¹ Korea Institute of Science and Technology Information, Daejeon, Republic of Korea
⁷² Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-Alpes, CNRS-IN2P3, Grenoble, France
⁷³ Lawrence Berkeley National Laboratory, Berkeley, California, USA
⁷⁴ Division of Particle Physics, Department of Physics, Lund University, Lund, Sweden
⁷⁵ Nagasaki Institute of Applied Science, Nagasaki, Japan
⁷⁶ Nara Women’s University (NWU), Nara, Japan
⁷⁷ Department of Physics, National and Kapodistrian University of Athens, School of Science, Athens, Greece
⁷⁸ National Centre for Nuclear Research, Warsaw, Poland
⁷⁹ National Institute of Science Education and Research, Homi Bhabha National Institute, Jatni, India
⁸⁰ National Nuclear Research Center, Baku, Azerbaijan
⁸¹ National Research and Innovation Agency-BRIN, Jakarta, Indonesia
⁸² Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
⁸³ Nikhef, National Institute for Subatomic Physics, Amsterdam, The Netherlands
⁸⁴ Nuclear Physics Group, STFC Daresbury Laboratory, Daresbury, UK
⁸⁵ Nuclear Physics Institute of the Czech Academy of Sciences, Husinec-Řež, Czech Republic
⁸⁶ Oak Ridge National Laboratory, Oak Ridge, TN, USA
⁸⁷ Ohio State University, Columbus, OH, USA
⁸⁸ Physics Department, Faculty of Science, University of Zagreb, Zagreb, Croatia
⁸⁹ Physics Department, Panjab University, Chandigarh, India
⁹⁰ Physics Department, University of Jammu, Jammu, India
⁹¹ Physics Program and International Institute for Sustainability with Knotted Chiral Meta Matter (SKCM2), Hiroshima University, Hiroshima, Japan
⁹² Physikalisches Institut, Eberhard-Karls-Universität Tübingen, Tübingen, Germany
⁹³ Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
⁹⁴ Physik Department, Technische Universität München, Munich, Germany
⁹⁵ Politecnico di Bari and Sezione INFN, Bari, Italy
⁹⁶ Research Division and ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
⁹⁷ Saga University, Saga, Japan
⁹⁸ Saha Institute of Nuclear Physics, Homi Bhabha National Institute, Kolkata, India
⁹⁹ School of Physics and Astronomy, University of Birmingham, Birmingham, UK
¹⁰⁰ Sección Física, Departamento de Ciencias, Pontificia Universidad Católica del Perú, Lima, Peru
¹⁰¹ Stefan Meyer Institut für Subatomare Physik (SMI), Vienna, Austria
¹⁰² SUBATECH, IMT Atlantique, Nantes Université, CNRS-IN2P3, Nantes, France
¹⁰³ Sungkyunkwan University, Suwon, Republic of Korea
¹⁰⁴ Suranaree University of Technology, Nakhon Ratchasima, Thailand
¹⁰⁵ Technical University of Košice, Košice, Slovak Republic
¹⁰⁶ The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland
¹⁰⁷ The University of Texas at Austin, Austin, TX, USA
¹⁰⁸ Universidad Autónoma de Sinaloa, Culiacán, Mexico
¹⁰⁹ Universidade de São Paulo (USP), São Paulo, Brazil
¹¹⁰ Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil
¹¹¹ Universidade Federal do ABC, Santo Andre, Brazil
¹¹² Universitatea Nationala de Stiinta si Tehnologie Politehnica Bucuresti, Bucharest, Romania
¹¹³ University of Cape Town, Cape Town, South Africa
¹¹⁴ University of Derby, Derby, UK
¹¹⁵ University of Houston, Houston, TX, USA
¹¹⁶ University of Jyväskylä, Jyväskylä, Finland
¹¹⁷ University of Kansas, Lawrence, KS, USA
¹¹⁸ University of Liverpool, Liverpool, UK
¹¹⁹ University of Science and Technology of China, Hefei, China
¹²⁰ University of South-Eastern Norway, Kongsberg, Norway
¹²¹ University of Tennessee, Knoxville, TN, USA
¹²² University of the Witwatersrand, Johannesburg, South Africa
¹²³ University of Tokyo, Tokyo, Japan
¹²⁴ University of Tsukuba, Tsukuba, Japan
¹²⁵ Universität Münster, Institut für Kernphysik, Münster, Germany
¹²⁶ Université Clermont Auvergne, CNRS/IN2P3, LPC, Clermont-Ferrand, France
¹²⁷ Université de Lyon, CNRS/IN2P3, Institut de Physique des 2 Infinis de Lyon, Lyon, France
¹²⁸ Université de Strasbourg, CNRS, IPHC UMR 7178, 67000, Strasbourg, France
¹²⁹ Université Paris-Saclay, Centre d’Etudes de Saclay (CEA), IRFU, Départment de Physique Nucléaire (DPhN), Saclay, France
¹³⁰ Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
¹³¹ Università degli Studi di Foggia, Foggia, Italy
¹³² Università del Piemonte Orientale, Vercelli, Italy
¹³³ Università di Brescia, Brescia, Italy
¹³⁴ Variable Energy Cyclotron Centre, Homi Bhabha National Institute, Kolkata, India
¹³⁵ Warsaw University of Technology, Warsaw, Poland
¹³⁶ Wayne State University, Detroit, MI, USA
¹³⁷ Yale University, New Haven, CT, USA
¹³⁸ Yildiz Technical University, Istanbul, Turkey
¹³⁹ Yonsei University, Seoul, Republic of Korea
¹⁴⁰ Affiliated with an Institute Covered by a Cooperation Agreement with CERN, Geneva, Switzerland
¹⁴¹ Affiliated with an International Laboratory Covered by a Cooperation Agreement with CERN, Geneva, Switzerland
¹⁴² Max-Planck-Institut fur Physik, Munich, Germany
¹⁴³ Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Bologna, Italy
¹⁴⁴ Dipartimento DET del Politecnico di Torino, Turin, Italy
¹⁴⁵ Yildiz Technical University, Istanbul, Turkey
¹⁴⁶ Department of Applied Physics, Aligarh Muslim University, Aligarh, India
¹⁴⁷ Institute of Theoretical Physics, University of Wroclaw, Wroclaw, Poland
¹⁴⁸ An Institution Covered by a Cooperation Agreement with CERN, Geneva, Switzerland
¹⁴⁹ CERN, 1211, Geneva 23, Switzerland

^a alice-publications@cern.ch

Received: 3 October 2024
Accepted: 21 February 2025
Published online: 19 May 2025

Abstract

The ALICE Collaboration at the CERN LHC has measured the inclusive production cross section of isolated photons at midrapidity as a function of the photon transverse momentum ($p_{\text{T}}^{\gamma }$), in Pb–Pb collisions in different centrality intervals, and in pp collisions, at centre-of-momentum energy per nucleon pair of $\sqrt{s_{\text{NN}}}=5.02$ TeV. The photon transverse momentum range is between 10–14 and 40–140 GeV/$c$, depending on the collision system and on the Pb–Pb centrality class. The result extends to lower $p_{\text{T}}^{\gamma }$ than previously published results by the ATLAS and CMS experiments at the same collision energy. The covered pseudorapidity range is $|{\eta }^{\gamma }|<0.67$. The isolation selection is based on a charged particle isolation momentum threshold $p_{\text{T}}^{\mathrm{iso},\mathrm{ch}}=1.5$ GeV/$c$ within a cone of radii $R=0.2$ and 0.4. The nuclear modification factor is calculated and found to be consistent with unity in all centrality classes, and also consistent with the HG-PYTHIA model, which describes the event selection and geometry biases that affect the centrality determination in peripheral Pb–Pb collisions. The measurement is compared to next-to-leading order perturbative QCD calculations and to the measurements of isolated photons and Z$_{}^0$ bosons from the CMS experiment, which are all found to be in agreement.