Measurement of the v₂ of π⁰ mesons produced in √S_NN 2.76 TeV PbPb collisions at the Large Hadron Collider

Abstract

We have performed the first measurement of the azimuthal anisotropy of neutral pions in relativistic heavy ion collisions in the CMS detector at the LHC. The data presented are from PbPb collisions at a center of mass energy per nucleon √S_NN = 2.76 TeV, in the range 20-80% centrality and from 1.6 - 8.0 GeV/c in pT. The amplitude of the second Fourier component v₂ of the π⁰ mesons was extracted via the event-plane method, and is presented as a function of π⁰ pT in a set of 10% centrality bins. We see a rise in the amplitude of from 1.6 to 3 GeV/c in pT where the amplitude reaches a maximum, and then gradually decreases towards 8 GeV/c in pT. A comparison is presented with the v₂ of inclusive charged particles in the CMS detector measured via the event-plane method in PbPb collisions at √S_NN = 2.76 TeV, as well as v₂ of neutral pions measured at RHIC by the PHENIX experiment in AuAu collisions at √S_NN = 200 GeV. The significance of the results is discussed with respect to the evolution of the strongly-coupled quark gluon plasma produced in relativistic heavy ion collisions.