Bochum 2018 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 2: Heavy Ion Collisions and QCD Phases I

HK 2.3: Talk

Monday, February 26, 2018, 14:45–15:00, HZO 60

Measurement of Neutral Mesons and Direct Photons in pp Collisions with ALICE at the LHC — •Daniel Mühlheim for the ALICE collaboration — Institut für Kernphysik, WWU Münster

ALICE has published the invariant cross sections for the production of π⁰ and η mesons in proton-proton collisions at √s = 0.9 TeV, 2.76 TeV, 7 TeV and most recently 8 TeV. Neutral mesons are reconstructed by means of three different detection systems; using the central barrel tracking detectors of ALICE in order to reconstruct photon conversions (PCM) and the two available calorimeters in the experiment, namely the PHOS and the EMCal. The reported measurements are carried out as well using a ’hybrid’ system which reconstructs meson candidates by combining one EMCal photon with one PCM photon. Thus, this ’hybrid’ system serves as an important cross-check and additionally measures an almost independent set of meson candidates. By using EMCal and PHOS triggers in addition, transverse momenta up to 40 GeV/c can be covered with the available statistics in the given datasets. In addition, the corresponding η/π⁰-ratios will be shown to test scaling laws for particle production. All obtained results will be compared with different Monte Carlo generators as well as recent NLO pQCD predictions.

Based on the obtained results, inclusive direct photon measurements are being carried out, for which the most recent status will be presented. A novel method using the ’hybrid’ PCM-EMCal system is followed in addition to tag π⁰ candidates and extract the direct photon signal, which will be shortly illustrated.