Measurement of Direct Photons in pp and Pb-Pb Collisions with ALICE

Wilde, M. R. and Abelev, B. and Adam, J. and Adamová, D. and Adare, A. M. and Aggarwal, M. M. and Aglieri, R. G. and Agócs, András and Agostinelli, A. and Aguilar, S. S. and Ahammed, Z. and Ahmad, A. and Ahmad, N. and Ahn, S. A. and Ahn, S. U. and Akindinov, A. and Aleksandrov, D. and Alessandro, B. and Alfaro, M. J. R. and Alici, A. and Alkin, A. and Alme, J. and Alt, T. and Altini, V. and Altinpinar, S. and Altsybeev, I. and Andrei, C. and Andronic, A. and Anguelov, V. and Anielski, J. and Barnaföldi, Gergely Gábor and Bencédi, Gyula and Berényi, Dániel and Boldizsár, László and Dénes, Ervin and Hamar, Gergő and Lévai, Péter and Pochybova, Sona (2013) Measurement of Direct Photons in pp and Pb-Pb Collisions with ALICE. NUCLEAR PHYSICS A, 904-90. 573C-576C. ISSN 0375-9474

Preview

Text 1210.5958v2.pdf Available under License Creative Commons Attribution. Download (955kB) | Preview

Abstract

The measurement of the direct photon transverse momentum spectrum in Pb-Pb collisions at √ sNN = 2.76 TeV with data taken by the ALICE experiment is presented. The measurement shows a clear direct-photon signal for 0-40% most central collisions below 4 GeV/c that can not be described by next-to-leading-order perturbative QCD (NLO pQCD) calculations. Above this value of pT the result is in agreement with pQCD predictions. The low pT signal is expected to have thermal photon contributions. The inverse slope parameter of an exponential fit is extracted as TLHC = 304±51syst+stat MeV. For a baseline measurement the analysis is performed for protonproton collisions at √ s = 7 TeV and for peripheral (40-80%) Pb-Pb collisions. Both results show no low pT direct-photon signal and are in agreement with pQCD calculations.

Actions (login required)

Edit Item