Direct photon measurements in pp and Pb-Pb collisions with the ALICE experiment

Abstract

Direct photon production in heavy-ion collisions provides a valuable set of observables to study the hot QCD medium. The direct photons are produced at different stages of the collision and escape the medium unaffected. In heavy-ion collisions, the direct photon yield at high transverse momentum (pT > 5 GeV/c) is dominated by prompt photons produced in hard scattering of incoming partons and provides information on nuclear parton distribution functions and on the initial parton dynamics. The low momentum component (pT_ 5 GeV/c) of the direct photon production is dominated by thermal radiation by the hot and dense matter created, carrying information on its space-time evolution, collective flow and temperature. We present recent ALICE results on direct photon production Pb-Pb collisions at 2.76 TeV and on direct photon production in pp at 7 TeV using isolation techniques. The results are compared to theoretical predictions and previous measurements