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# Measurement of high p_T isolated prompt photons in lead-lead collisions at sqrt(s_NN)=2.76 TeV with the ATLAS detector at the LHC

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### Abstract

Prompt photons are a powerful tool to study heavy ion collisions. Their production rates provide access to the initial state parton distribution functions and also provide a means to calibrate the expected energy of jets that are produced in the medium. The ATLAS detector measures photons with its hermetic, longitudinally segmented calorimeter, which gives excellent spatial and energy resolutions, and detailed information about the shower shape of each measured photon. This provides significant rejection against the expected background from the decays of neutral pions in jets. Rejection against jet fragmentation products is further enhanced by requiring candidate photons to be isolated. First results on the spectra of isolated prompt photons from a dataset with an integrated luminosity of approximately 0.13 nb^-1 of lead-lead collisions at sqrt(s_NN)=2.76 TeV are shown as a function of transverse momentum and centrality. The measured spectra are compared to expectations from perturbative QCD calculations.

### Most cited references2

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### Jet Quenching in the Opposite Direction of a Tagged Photon in High-Energy Heavy-Ion Collisions

(1996)
We point out that events associated with large $$E_T$$ direct photons in high-energy heavy-ion collisions can be used to study jet energy loss in dense matter. In such events, the $$p_T$$ spectrum of charged hadrons from jet fragmentation in the opposite direction of the tagged photon is estimated to be well above the background which can be reliably subtracted at moderately large $$p_T$$. We demonstrate that comparison between the extracted fragmentation function in $$AA$$ and $$pp$$ collisions can be used to determine the jet energy loss and the interaction mean-free-path in the dense matter produced in high-energy heavy-ion collisions.
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### A new critical study of photon production in hadronic collisions

(2006)
In the light of the new prompt photon data collected by PHENIX at RHIC and by D0 at the run II of the Tevatron, we revisit the world prompt photon data, both inclusive and isolated, in hadronic collisions, and compare them with the NLO QCD calculations implemented in the Monte Carlo programme JETPHOX.
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### Author and article information

###### Journal
21 September 2012
###### Article
1209.4910