Studies of jet quenching using isolated-photon+jet correlations in PbPb and pp collisions at √sNN=2.76 TeV

Chatrchyan, S. and Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Bergauer, T. and Dragicevic, M. and Erö, J. and Fabjan, C. and Friedl, M. and Frühwirth, R. and Ghete, V. M. and Hammer, J. and Hörmann, N. and Hrubec, J. and Jeitler, M. and Kiesenhofer, W. and Knünz, V. and Krammer, M. and Liko, D. and Mikulec, I. and Pernicka, M. and Rahbaran, B. and Rohringer, C. and Rohringer, H. and Schöfbeck, R. and Strauss, J. and Taurok, A. and Wagner, P. and Waltenberger, W. and Bencze, György and Hajdu, Csaba and Hidas, Pál and Horváth, Dezső and Krajczár, Krisztián and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Béni, Noémi Tekla and Czellár, Sándor and Molnár, József and Pálinkás, József and Szillási, Zoltán and Karancsi, János and Raics, Péter and Trócsányi, Zoltán and Ujvári, Balázs and Veres, Gábor (2013) Studies of jet quenching using isolated-photon+jet correlations in PbPb and pp collisions at √sNN=2.76 TeV. PHYSICS LETTERS B, 718 (3). pp. 773-794. ISSN 0370-2693

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Abstract

Results from the first study of isolated-photon+jet correlations in relativistic heavy ion collisions are reported. The analysis uses data from PbPb collisions at a centre-of- mass energy of 2.76 TeV per nucleon pair corresponding to an integrated luminosity of 150 μb−1 recorded by the CMS experiment at the LHC. For events containing an isolated photon with transverse momentum pγ T > 60 GeV/c and an associated jet with pJet T > 30 GeV/c, the photon+jet pT imbalance is studied as a function of collision cen- trality and compared to pp data and PYTHIA calculations at the same collision energy. Using the pγ T of the isolated photon as an estimate of the momentum of the associated parton at production, this measurement allows a characterisation of the in-medium parton energy loss. For more central PbPb collisions, a significant decrease in the ratio pJet T /pγ T relative to that in the PYTHIA reference is observed. Furthermore, signif- icantly more pγ T > 60 GeV/c photons in PbPb are observed not to have an associated pJet T > 30 GeV/c jet, compared to the reference. However, no significant broadening of the photon+jet azimuthal correlation is observed.

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