Azimuthal Anisotropy of Charged Particles at High Transverse Momenta in Pb-Pb Collisions at √s_(NN) = 2.76 TeV

Creators: Chatrchyan, S.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Di Marco, E.; Duarte, J.; Gataullin, M.; Ma, Y.; Mott, A.; Newman, H. B.; Rogan, C.; Shin, K.; Timciuc, V.; Traczyk, P.; Veverka, J.; Wilkinson, R.; Yang, Y.; Zhu, R. Y.; Spiropulu, M.; Dias, F. A.; CMS Collaboration

Abstract

The azimuthal anisotropy of charged particles in Pb-Pb collisions at √s_(NN)=2.76 TeV is measured with the CMS detector at the LHC over an extended transverse momentum (p_T) range up to approximately 60 GeV/c. The data cover both the low-p_T region associated with hydrodynamic flow phenomena and the high-p_T region where the anisotropies may reflect the path-length dependence of parton energy loss in the created medium. The anisotropy parameter (v_2) of the particles is extracted by correlating charged tracks with respect to the event-plane reconstructed by using the energy deposited in forward-angle calorimeters. For the six bins of collision centrality studied, spanning the range of 0–60% most-central events, the observed v_2 values are found to first increase with pT, reaching a maximum around p_T=3 GeV/c, and then to gradually decrease to almost zero, with the decline persisting up to at least p_T=40 GeV/c over the full centrality range measured.

Additional Information

© 2012 CERN, for the CMS Collaboration. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Received 9 April 2012; published 10 July 2012. 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); Academy of Sciences and NICPB (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); SCSR (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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