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

H. Abramowicz, M. J. Alconada Verzini, L. Barak, G. Bella, H. Cohen, E. Etzion, M. S. Lutz, D. Reikher, A. Soffer, N. M. Tamir

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish
Article number014903
JournalPhysical Review C
Volume104
Issue number1
DOIs
StatePublished - Jul 2021

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