Measurement of the production cross section of an isolated photon associated with jets in proton-proton collisions at sqrt(s) = 7 TeV with the ATLAS detector

TL;DR

This paper measures the production cross section of isolated photons with jets in proton-proton collisions at 7 TeV, comparing results with QCD predictions and analyzing different jet rapidity ranges and photon energies.

Contribution

First measurement of isolated photon plus jet cross sections at 7 TeV with detailed rapidity and energy dependence, testing perturbative QCD predictions.

Findings

NLO QCD calculations agree with data at high energies

Discrepancies observed for photon energies below ~45 GeV

Differential cross sections vary with jet rapidity ranges

Abstract

A measurement of the cross section for the production of an isolated photon in association with jets in proton-proton collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. Photons are reconstructed in the pseudorapidity range |eta(gamma)|<1.37 and with a transverse energy E_T(gamma)>25 GeV. Jets are reconstructed in the rapidity range |y(jet)|<4.4 and with a transverse momentum p_T(jet)>20 GeV. The differential cross section dsigma/dE_T(gamma) is measured, as a function of the photon transverse energy, for three different rapidity ranges of the leading-p_T jet: |y(jet)|<1.2, 1.2<=|y(jet)|<2.8 and 2.8<=|y(jet)|< 4.4. For each rapidity configuration the same-sign (eta(gamma)y(jet)>=0) and opposite-sign (eta(gamma)y(jet)<0) cases are studied separately. The results are based on an integrated luminosity of 37 pb^-1, collected with the ATLAS detector at the LHC. Next-to-leading order perturbative QCD calculations are found to be in fair agreement with the data, except for E_T(gamma)<~45 GeV, where the theoretical predictions overestimate the measured cross sections.