Measurement of the correlation of jets with high $p_{T}$ isolated prompt photons in lead-lead collisions at $sqrt{s_{NN}} =2.76}$ TeV with the ATLAS detector at the LHC

Prompt photons produced in heavy ion collisions are the golden channel for studying the effects of jet quenching in the hot, dense medium. Photons provide a means to calibrate the expected energy of jets that are produced in the medium, and thus are a tool to probe the physics of jet quenching more precisely both through jet spectra and fragmentation properties. The ATLAS detector measures photons with its hermetic, longitudinally segmented calorimeter, which gives excellent spatial and energy resolution, and detailed information about the shower shape of each measured photon. This gives significant rejection against the expected background from neutral pions in jets. Rejection against jet fragmentation products is further enhanced by isolation criteria, which can be based on calorimeter energy or the presence of high $p_T$ tracks. Jets are measured with the anti-$k_t$ algorithm for three different radii and their performance in photon-jet events been assessed quantitatively. First results on the correlation of back-to-back isolated prompt photons with jets from approximately 0.13 nb$^{-1}$ of lead-lead data are shown, as a function of transverse momentum and centrality. The photons are selected to have $p_T = 60-90$ GeV and $|eta|<1.3$. The jets have $p_T>25$ GeV and $|eta|<2.1$. The measured spectra are corrected to remove the effect of detector acceptance and resolution compared to expectations from PYTHIA. Centrality-dependent shifts in the mean fractional energy carried by the jet ($x_{Jgamma}$) and the per-photon jet yield ($R_{Jgamma}$) are observed.No corresponding changes are seen in the $Delta phi_{Jgamma}$ distributions.