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Published January 8, 2013 | Published
Journal Article Open

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


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 p^γ_T > 60 GeV/c and an associated jet with p^(Jet)_T > 30 GeV/c, the photon+ jet p_T imbalance is studied as a function of collision centrality and compared to pp data and pythia calculations at the same collision energy. Using the p^γ_T of the isolated photon as an estimate of the momentum of the associated parton at production, this measurement allows an unbiased characterisation of the in-medium parton energy loss. For more central PbPb collisions, a significant decrease in the ratio p^(Jet)_T /p^γ_T relative to that in the PYTHIA reference is observed. Furthermore, significantly more p^γ_T > 60 GeV/c photons in PbPb are observed not to have an associated p^(Jet)_T > 30 GeV/c jet, compared to the reference. However, no significant broadening of the photon +jet azimuthal correlation is observed.

Additional Information

© 2012 CERN for the benefit of the CMS Collaboration. Published by Elsevier B.V. Received 1 May 2012. Received in revised form 18 July 2012. Accepted 2 November 2012. Available online 6 November 2012. Editor: M. Doser. This article is published Open Access at sciencedirect.com. It is distributed under the terms of the Creative Commons Attribution License 3.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited. We congratulate our colleagues in the CERN accelerator departments for the excellent performance of the LHC machine. We thank the technical and administrative staff at CERN and other CMS institutes, and acknowledge support from: FMSR (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); MoER, SF0690030s09 and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); MSI (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MON, RosAtom, RAS and RFBR (Russia); MSTD (Serbia); MICINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United Kingdom); DOE and NSF (USA).

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