Measurement of jet quenching in direct photon-jet events in lead-lead collisions at $\sqrt {s_{NN} } =2.76\mbox{ TeV}$

Direct photons are an important resource for studying the physics of jet quenching in heavy ion collisions. Recent measurements have shown that jets lose energy when traveling through a dense QCD medium; isolated photons can be used to calibrate the associated jet energy and evaluate the extent of quenching. In this analysis, results will be presented for measurements of photon-jet correlations using approximately $140\mbox{ }\mu b^{-1}$ of data from lead-lead collisions at nucleon center-of-mass energy $\sqrt {s_{NN} } =2.76\mbox{ TeV}$, recorded by the ATLAS detector at the Large Hadron Collider. Events that have isolated prompt photons with transverse momentum $p_T >65\mbox{ GeV}$ opposite jets with $p_T >25\mbox{ GeV}$ are considered, and the transverse momentum imbalance is quantified by means of the ratio $X_{J\gamma } =p_T^{\mbox{jet}} /p_T^\gamma $ for different collision centralities, photon energy bins and angular cuts. Background subtraction, efficiency, unfolding and jet-scale corrections are applied to the measured distributions, which are compared in turn to perturbative QCD calculations.