Inclusive photon multiplicity at forward pseudorapidities in pp and p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with ALICE

TL;DR

This paper measures inclusive photon multiplicity at forward pseudorapidities in pp and p-Pb collisions at 5.02 TeV using ALICE, providing insights into initial collision stages and nuclear matter effects.

Contribution

It presents the first detailed pseudorapidity distributions of inclusive photons at forward angles in these collisions, comparing with charged particles and theoretical models.

Findings

Photon multiplicity distributions are consistent with certain Monte Carlo models.

Photon production shows specific dependence on collision system and multiplicity.

Results help constrain models of initial collision dynamics.

Abstract

Global observables such as the pseudorapidity distributions of particle multiplicities in the final state are crucial to shed light into the physics processes involved in hadronic collisions. In proton$-$lead (p$-$Pb) collisions at Large Hadron Collider (LHC) energies, such measurements provide an important baseline to understand lead$-$lead (Pb$-$Pb) results by disentangling hot nuclear matter effects from the ones due to the cold nuclear matter. Multiplicity measurements can also put constraints on theoretical models describing the initial stages of the collision, e.g., to what degree the nucleon and the nuclei interact as dilute (partons) or dense (CGC-like) fields. The study of inclusive photon multiplicity aims to provide complementary measurements to those obtained with charged particles. In these proceedings, the pseudorapidity distributions of inclusive photons at forward pseudorapidity ($2.3 < \eta_{\rm lab} < 3.9$) in pp and p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV are presented. The data samples were collected using the Photon Multiplicity Detector (PMD) of ALICE. The multiplicity dependence of photon production in p$-$Pb collisions is presented and a comparison with charged-particle distributions measured at mid-pseudorapidity is shown. The results are also compared with predictions from Monte Carlo event generators.