Centrality, rapidity and p(T) dependence of isolated prompt photon production in lead-lead collisions at root(NN)-N-S=2.76 TeV with the ATLAS detector at the LHC

摘要

The ATLAS experiment at the LHC has measured prompt photon production in root(NN)-N-S = 2.76 TeV Pb + Pb collisions using data collected in 2011 with an integrated luminosity of 0.14 nb(-1). The measurement is performed with a hermetic, longitudinally segmented calorimeter, which gives excellent spatial and energy resolution, and detailed information about the shower shape of each measured photon. Using a selection based on shower shapes and an isolation criterion gives measured purities between approximately 50-90%, depending on p(T), eta and centrality. Photon yields, scaled by the mean nuclear thickness function, are determined as a function of collision centrality, pseudorapidity (in two intervals vertical bar eta vertical bar < 1.37 and 1.52 < vertical bar eta vertical bar < 2.37) and transverse momentum (22 < p(T) < 280 GeV). The scaled yields are shown compared to expectations from JETPHOX (perturbative QCD calculations at next to leading order), as are the ratios of the forward yields to those near mid-rapidity (for 22 < p(T) < 140 GeV). The observed photon yields agree well with the predictions for proton proton within statistical and systematic uncertainties, but are unable to distinguish between these calculations and others including isospin and nuclear PDF effects. (C) 2014 CERN. Published by Elsevier B.V. All rights reserved.