Investigations of anisotropic flow using multiparticle azimuthal correlations in pp, p−Pb, Xe-Xe, and Pb-Pb collisions at the LHC

Abstract

Measurements of anisotropic flow coefficients ( v n ) and their cross-correlations using two- and multiparticle cumulant methods are reported in collisions of pp at √ s = 13 TeV , p− Pb at a center-of-mass energy per nucleon pair √ s NN = 5.02 TeV , Xe-Xe at √ s NN = 5.44 TeV , and Pb-Pb at √ s NN = 5.02 TeV recorded with the ALICE detector. The multiplicity dependence of vn is studied in a very wide range from 20 to 3000 particles produced in the midrapidity region |η | < 0.8 for the transverse momentum range 0.2 < p T < 3.0 GeV / c . An ordering of the coefficients v2>v3>v4 is found in pp and p− Pb collisions, similar to that seen in large collision systems, while a weak v2 multiplicity dependence is observed relative to nucleus-nucleus collisions in the same multiplicity range. Using a novel subevent method, v2 measured with four-particle cumulants is found to be compatible with that from six-particle cumulants in pp and p− Pb collisions. The magnitude of the correlation between v2n and v2m, evaluated with the symmetric cumulants SC ( m , n ) is observed to be positive at all multiplicities for v2 and v4, while for v2 and v3 it is negative and changes sign for multiplicities below 100, which may indicate a different vn fluctuation pattern in this multiplicity range. The observed long-range multiparticle azimuthal correlations in high multiplicity pp and p− Pb collisions can neither be described by pythia 8 nor by impact-parameter-Glasma, music, and ultrarelativistic quantum molecular dynamics model calculations, and hence, provide new insights into the understanding of collective effects in small collision systems.