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

Abstract

The azimuthal anisotropy of charged particles in Pb-Pb collisions at sqrt[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 (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 p(T), 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 pp(T)=40 GeV/c over the full centrality range measured.

Corona effect in AA collisions at the LHC

“…Thus, v 2 should drop to about a factor of 2. This what is qualitatively seen by the three experiments [12,14,15].…”

“…In Fig. 5 we compare our estimations with CMS results at p t =15 GeV/c [12]. The prediction of a large v 2 even at LHC is confirmed, the sensitivity to the collision geometry persists up to high p t .…”

Systematic studies of correlations between different order flow harmonics in Pb-Pb collisions at sNN=2.76 TeV

“…Difference in pressure gradients and the interactions among matter constituents produced in the spatially anisotropic overlap region of the two colliding nuclei result in anisotropic transverse flow in the momentum space. The large elliptic flow discovered at RHIC energies [3][4][5][6][7] is also observed at LHC energies [8][9][10][11][12][13][14][15][16][17][18]. The measurements are well described by calculations utilizing viscous hydrodynamics [19][20][21][22][23][24].…”

Jet quenching as a probe of the initial stages in heavy-ion collisions

“…This corresponds to the set-up employed in any approach that aims to describe the jet harmonics coefficients using a smooth dependence of the medium parameter on the medium properties [19,26,27]. [20,[42][43][44]. The blue solid, τq = 0 fm, dotted green, τq = 0.197 fm, and dashed purple, τq = 0.572 fm, lines correspond, respectively, to Cases i), ii) and iii) of the early times treatment.…”