Azimuthal anisotropy of charged particles with transverse momentum up to 100 GeV/c in PbPb collisions at √SNN = 5.02TeV

Abstract

The Fourier coefficients v[subscript 2] and v[subscript 3] characterizing the anisotropy of the azimuthal distribution of charged particles produced in PbPb collisions at √sNN =5.02 TeV are measured with data collected by the CMS experiment. The measurements cover a broad transverse momentum range, 1 < p[subscript T] < 100 GeV/c. The analysis focuses on the p[subscript T] > 10 GeV/c range, where anisotropic azimuthal distributions should reflect the path-length dependence of parton energy loss in the created medium. Results are presented in several bins of PbPb collision centrality, spanning the 60% most central events. The v[subscript 2] coefficient is measured with the scalar product and the multiparticle cumulant methods, which have different sensitivities to initial-state fluctuations. The values from both methods remain positive up to p[subscript T] ∼60–80 GeV/c, in all examined centrality classes. The v[subscript 3] coefficient, only measured with the scalar product method, tends to zero for p[subscript T] ≳20 GeV/c. Comparisons between theoretical calculations and data provide new constraints on the path-length dependence of parton energy loss in heavy ion collisions and highlight the importance of the initial-state fluctuations. Keywords: CMS, QGP, High-pT, Flow, Parton energy loss, Jet quenching