Darmstadt 2016 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 56: Heavy Ion Collision and QCD Phases XI

HK 56.3: Talk

Thursday, March 17, 2016, 17:00–17:15, S1/01 A01

Photon HBT with ALICE — •Hans Beck for the ALICE collaboration — Physikalisches Institut, University of Heidelberg

Photon-photon correlations at small relative momentum carry a distinct signal from the quantum statistical interference of the photons’ wave functions. Being sensitive to the size of the emitter, these photon correlations bear the unique opportunity to directly study the supposedly hydrodynamical evolution of the source beyond kinetic freeze-out. This qualitatively distinguishes two-photon correlations from hadron femtoscopy.

ALICE at the LHC allows to observe photons via their conversion to charged leptons reconstructed with the tracking detectors and the direct identification in its electromagnetic calorimeters. An experimental advantage is the absence of two-particle resolution effects when combining the two methods.

We present correlation functions of photon candidates from the Run 1 Pb-Pb dataset and quantify the clear signal at zero relative momentum in terms of its height and width differentially in pair transverse momentum over a range of several GeV/c. We prove previously neglected processes to significantly contribute by rejecting them via specific two-particle criteria and presenting the impact on the correlation function. An outlook is given.