Two- and Multi-particle Azimuthal Correlations in Small Collision Systems with the ATLAS Detector

The recent ATLAS results on two- and multi-particle azimuthal correlations of charged particles are presented for s=5.02 TeV and 13 TeV pp, sNN=5.02 TeV p+Pb and sNN=2.76 TeV low-multiplicity Pb+Pb collisions. To suppress the “non-flow” contribution from the correlations, a template fitting procedure is used in the two-particle correlations (2PC) measurements, while for multi-particle correlations the cumulant method is applied. The correlations are expressed in the form of Fourier harmonics vn(n=2,3,4) measuring the global azimuthal anisotropy of produced particles. The measurements presented hereafter confirm the evidence for collective phenomena in high-multiplicity p+Pb and low-multiplicity Pb+Pb collisions. For pp collisions the results on four-particle cumulants do not demonstrate a similar collective behaviour.