Dresden 2013 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 40: Schwerionenkollisionen und QCD Phasen
HK 40.5: Talk
Tuesday, March 5, 2013, 18:00–18:15, HSZ-204
Measurement of direct photons in pp and Pb-Pb collisions with ALICE — •Martin Wilde — WWU Münster
Direct photons are an important probe in diagnosing the highly excited state of nuclear matter created in heavy-ion collisions: They provide access to various stages of the collision including the initial state.
The ALICE detector is equipped with two high resolution electromagnetic calorimeters and a central tracking system that make it well suited to study direct photon production over a brought rang of pT. In addition to classical calorimeter measurements, the low pT regime can be targeted via the measurement of photon conversion products by the ALICE TPC with high tracking efficiency.
In this talk the analysis of direct photon production in pp (at √s = 7 TeV and √s =2.76 TeV) and Pb-Pb (at √sNN = 2.76 TeV) collisions is presented. The inclusive photon and neutral pion spectrum is measured via photon conversions in the ALICE setup. From the neutral pion yield a decay photon cocktail is deduced. The signal is obtained by calculating the double ratio (γ/π0)/(γdecay/π0). Implications on the search for a direct photon excess at low pT will be discussed.