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

This paper presents the measurement of charged-hadron and identified-hadron (𝐾0
S, Λ, Ξ−) yields in photonuclear collisions using 1.7nb−1 of √𝑠𝑁⁢𝑁=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 √𝑠𝑁⁢𝑁=5.02TeV 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.