Centrality, rapidity and transverse momentum dependence of isolated prompt photon production in lead-lead collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV measured with the ATLAS detector

TL;DR

This paper measures isolated prompt photon production in lead-lead collisions at 2.76 TeV with the ATLAS detector, comparing results to pQCD predictions and nuclear modifications to understand nuclear effects on photon yields.

Contribution

It provides the first detailed measurement of prompt photon yields as a function of centrality and pseudorapidity in Pb+Pb collisions at this energy, testing nuclear parton distribution functions.

Findings

Measured photon yields agree with pQCD predictions within uncertainties.

Yields and ratios are consistent with models including nuclear modifications.

Provides data for constraining nuclear PDFs in heavy-ion collisions.

Abstract

Prompt photon production in $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV Pb+Pb collisions has been measured by the ATLAS experiment at the Large Hadron Collider using data collected in 2011 with an integrated luminosity of 0.14 nb$^{-1}$. Inclusive photon yields, scaled by the mean nuclear thickness function, are presented as a function of collision centrality and transverse momentum in two pseudorapidity intervals, $|\eta| < 1.37$ and $1.52 < |\eta| < 2.37$. The scaled yields in the two pseudorapidity intervals, as well as the ratios of the forward yields to those at midrapidity, are compared to the expectations from next-to-leading order perturbative QCD calculations from JETPHOX. The measured cross sections agree well with the predictions for proton-proton collisions within statistical and systematic uncertainties. Both the yields and ratios are also compared to two other pQCD calculations, one which uses the isospin content appropriate to colliding lead nuclei, and another which includes the EPS09 nuclear modifications to the nucleon parton distribution functions.