Systematics of azimuthal anisotropy harmonics in proton–nucleus collisions at the LHC from the Color Glass Condensate

Abstract

Simple power counting arguments in the dilute-dense framework of the Color Glass Condensate (CGC) Effective Field Theory predict that even and odd azimuthal anisotropy harmonics of two-particle correlations in proton–nucleus collisions at the LHC will respectively satisfy v2n2{2}∝Nch0 and v2n+12{2}∝Nch, where Nch denotes the number of charged particles. We show that these expectations are borne out qualitatively, and even quantitatively, within systematic uncertainties, for v2 and v4 in comparisons with data from the ATLAS collaboration. We also observe that ATLAS data for the v3 azimuthal harmonic are in excellent agreement with our qualitative expectation; quantitative comparisons are numerically challenging at present. The lessons from this study fully complement those gained by the recent comparison of the CGC dilute-dense framework [1] to data from the PHENIX collaboration on small system collisions at RHIC.