Charged-hadron and identified-hadron (K0S , , −) yield measurements in photonuclear Pb + Pb and p + Pb collisions at √sNN = 5.02 TeV with ATLAS

Abstract

This paper presents the measurement of charged-hadron and identified-hadron (K0S , , −) yields in photonuclearcollisions using 1.7 nb−1 of√sNN = 5.02 TeV Pb + Pb data collected in 2018 with the ATLAS detectorat the Large Hadron Collider. Candidate photonuclear events are selected using a combination of tracking andcalorimeter information, including the zero-degree calorimeter. The yields as a function of transverse momentumand rapidity are measured in these photonuclear collisions as a function of charged-particle multiplicity. Thesephotonuclear results are compared with 0.1nb−1 of√sNN = 5.02 TeV p + Pb data collected in 2016 by ATLASusing similar charged-particle multiplicity selections. These photonuclear measurements shed light on potentialquark-gluon plasma formation in photonuclear collisions via observables sensitive to radial flow, enhancedbaryon-to-meson ratios, and strangeness enhancement. The results are also compared with the Monte CarloDPMJET-III generator and hydrodynamic calculations to test whether such photonuclear collisions may producesmall droplets of quark-gluon plasma that flow collectively.