Mainz 2012 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 44: Schwerionenkollisionen und QCD Phasen

HK 44.3: Talk

Thursday, March 22, 2012, 17:15–17:30, P 5

Separation of decay photons and prompt photons in ALICE using a neural network — •Thomas Keuter — Institut für Kernphysik, WWU Münster, Deutschland

In this talk, the separation of decay photons and prompt photons in simulated proton-proton collisions at √s = 7 TeV in the ALICE experiment will be presented. The ALICE experiment investigates the quark-gluon plasma (QGP), created in central Pb-Pb-collisions at the LHC. Prompt photons are an ideal probe to investigate the QGP, since they do not interact strongly and are therefore mostly unaffected by a strongly interacting medium. They can be used as a reference for single particle spectra, because their R_AA should be equal to one. Moreover, the fragmentation function of hadrons can be calculated in γ-jet events if prompt photons can be identified and also jet-quenching in Pb-Pb collisions can be investigated. Photons from particle decays (mainly π⁰ and η) form a large background and these decay photons have to be separated from the prompt photons. In this talk, a neural network is used to distinguish between the photons on an event-by-event basis. The network can be trained with decay photons which are identified using an invariant mass analysis and with prompt photons using so-called random cones in minimum bias events.