Azimuthal Anisotropy of Charged Particles at High Transverse Momenta in Pb-Pb Collisions at √sNN=2.76  TeV

CMS Collaboration; Chatrchyan, S; Khachatryan, V; Aguiló, E; Amsler, C; Chiochia, V; De Visscher, S; Favaro, C; Ivova Rikova, M; Millan Mejias, B; Otiougova, P; Robmann, P; Snoek, H; Tupputi, S; Verzetti, M; et al (2012). Azimuthal Anisotropy of Charged Particles at High Transverse Momenta in Pb-Pb Collisions at √sNN=2.76 TeV. Physical Review Letters, 109(2):022301.

Abstract

The azimuthal anisotropy of charged particles in Pb-Pb collisions at √sNN=2.76  TeV is measured with the CMS detector at the LHC over an extended transverse momentum (pT) range up to approximately 60  GeV/c. The data cover both the low-pT region associated with hydrodynamic flow phenomena and the high-pT region where the anisotropies may reflect the path-length dependence of parton energy loss in the created medium. The anisotropy parameter (v2) 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 v2 values are found to first increase with pT, reaching a maximum around pT=3  GeV/c, and then to gradually decrease to almost zero, with the decline persisting up to at least pT=40  GeV/c over the full centrality range measured.

Abstract

The azimuthal anisotropy of charged particles in Pb-Pb collisions at √sNN=2.76  TeV is measured with the CMS detector at the LHC over an extended transverse momentum (pT) range up to approximately 60  GeV/c. The data cover both the low-pT region associated with hydrodynamic flow phenomena and the high-pT region where the anisotropies may reflect the path-length dependence of parton energy loss in the created medium. The anisotropy parameter (v2) 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 v2 values are found to first increase with pT, reaching a maximum around pT=3  GeV/c, and then to gradually decrease to almost zero, with the decline persisting up to at least pT=40  GeV/c over the full centrality range measured.

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