Two-particle azimuthal correlations in photonuclear ultraperipheral Pb+Pb collisions at 5.02 TeV with ATLAS

G Aad, Torsten Åkesson, Eric Edward Corrigan, Caterina Doglioni, Jannik Geisen, Eva Brottmann Hansen, Vincent Hedberg, Göran Jarlskog, Balazs Konya, Else Lytken, Katja Mankinen, Caterina Marcon, Ulf Mjörnmark, Geoffrey André Adrien Mullier, Ruth Pöttgen, Eleni Skorda, Oxana Smirnova, L Zwalinski, ATLAS Collaboration

Research output: Contribution to journalArticlepeer-review


Two-particle long-range azimuthal correlations are measured in photonuclear collisions using 1.7nb-1 of 5.02 TeV Pb+Pb collision data collected by the ATLAS experiment at the CERN Large Hadron Collider. Candidate events are selected using a dedicated high-multiplicity photonuclear event trigger, a combination of information from the zero-degree calorimeters and forward calorimeters, and from pseudorapidity gaps constructed using calorimeter energy clusters and charged-particle tracks. Distributions of event properties are compared between data and Monte Carlo simulations of photonuclear processes. Two-particle correlation functions are formed using charged-particle tracks in the selected events, and a template-fitting method is employed to subtract the nonflow contribution to the correlation. Significant nonzero values of the second- and third-order flow coefficients are observed and presented as a function of charged-particle multiplicity and transverse momentum. The results are compared with flow coefficients obtained in proton-proton and proton-lead collisions in similar multiplicity ranges, and with theoretical expectations. The unique initial conditions present in this measurement provide a new way to probe the origin of the collective signatures previously observed only in hadronic collisions. © 2021 CERN. CERN, for the ATLAS Collaboration. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Original languageEnglish
Article number014903
JournalPhysical Review C
Issue number1
Publication statusPublished - 2021

Subject classification (UKÄ)

  • Subatomic Physics


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