Charged-hadron and identified-hadron $(K_S^0, Λ, Ξ^−)$ yield measurements in photonuclear Pb+Pb and p+Pb collisions at $\sqrt{{s}_{NN}}$ = 5.02 TeV with ATLAS

This paper presents the measurement of charged-hadron and identified-hadron $(K_S^0, Λ, Ξ^−)$ yields in photonuclear collisions using 1.7 nb$^{−1}$ of $\sqrt{{s}_{NN}}$ = 5.02TeV Pb+Pb data collected in 2018 with the ATLAS detector at the Large Hadron Collider. Candidate photonuclear events are selected using a combination of tracking and calorimeter information, including the zero-degree calorimeter. The yields as a function of transverse momentum and rapidity are measured in these photonuclear collisions as a function of charged-particle multiplicity. These photonuclear results are compared with 0.1nb$^{−1}$ of $\sqrt{{s}_{NN}}$ = 5.02 TeV p+Pb data collected in 2016 by ATLAS using similar charged-particle multiplicity selections. These photonuclear measurements shed light on potential quark-gluon plasma formation in photonuclear collisions via observables sensitive to radial flow, enhanced baryon-to-meson ratios, and strangeness enhancement. The results are also compared with the Monte Carlo dpmjet-iii generator and hydrodynamic calculations to test whether such photonuclear collisions may produce small droplets of quark-gluon plasma that flow collectively.