Measurement of isolated photon production in pp and PbPb collisions at sqrt{sNN} =2.76$ TeV with CMS

TL;DR

This paper reports measurements of isolated photon production in proton-proton and lead-lead collisions at 2.76 TeV, showing results consistent with QCD predictions and no significant nuclear modification effects across centralities.

Contribution

First measurement of isolated photon production in PbPb collisions at this energy with detailed comparison to pp results and theoretical predictions.

Findings

Photon yields agree with NLO pQCD predictions.

PbPb to pp yield ratio is consistent with unity.

No significant nuclear modification observed.

Abstract

Isolated photon production is measured in pp and PbPb collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the pseudorapidity range |eta|<1.44 and transverse energies E_T between 20 and 80 GeV with the CMS detector at the LHC. The measured E_T spectra are found to be in good agreement with next-to-leading-order perturbative QCD predictions. The ratio of PbPb to pp isolated photon E_T-differential yields, scaled by the number of incoherent nucleon-nucleon collisions, is consistent with unity for all PbPb reaction centralities.