Direct photon production in pp, p-Pb and Pb-Pb collisions: results from ALICE

Abstract

Direct photon measurements provide a tool for testing QCD predictions in pp collisions and valuable information about properties of the quarkgluon matter created in nucleus-nucleus collisions. Comparing direct photon production in pp, p-Pb and Pb-Pb collisions, one can check the scaling with the number of binary collisions expected at high transverse momentum and get insight into the hot and cold hadronic matter properties with soft photons. The elliptic flow of direct photons is another unique possibility to trace the collective flow formation and space-time evolution of the fireball. We present the latest measurements of direct photon production in pp, p-Pb and Pb-Pb collisions and of the elliptic flow in Pb-Pb collisions at the LHC energies. Comparison to recent theory predictions will be also discussed.

Prompt photon production in high-energy pA collisions at forward rapidity

“…The published data from (dAu) PHENIX [45] and (pPb) ATLAS [34] are included. For the sake of illustration, we also included the preliminary data from PHENIX for pAu collisions ( √ s = 200 GeV) [55,56] as well as the preliminary ALICE pPb data ( √ s = 5.02 TeV) [57]. Interestingly, PHENIX Collaboration [56] has recently investigated the scaling of the direct photon yield, integrated for p T 1.0 GeV, as a function of charged-particle multiplicity, dN ch /dη| η=0 .…”