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HK: Fachverband Physik der Hadronen und Kerne

HK 40: Schwerionenkollisionen und QCD Phasen

HK 40.5: Vortrag

Dienstag, 5. März 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 p_T. In addition to classical calorimeter measurements, the low p_T 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 √s_NN = 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)/(γ_decay/π⁰). Implications on the search for a direct photon excess at low p_T will be discussed.