Measurement of the flow harmonic correlations in pp, p+Pb and low multiplicity Pb+Pb collisions with the ATLAS detector at the LHC

Recent measurements of the correlations between flow harmonics obtained using four-particle symmetric cumulants and three-particle asymmetric cumulants with the ATLAS detector at the LHC are described. The data sets of pp, p+Pb and peripheral Pb+Pb collisions at various energies are analyzed, aiming to probe the long-range collective nature of multi-particle production in small systems. The sensitivity of the standard cumulant method to non-flow correlations is investigated by introducing the subevents method. A systematic reduction of non-flow effects is observed when using the two-subevent method. Further reduction is observed with the three-subevent method that is consistent with the results obtained with the four-subevent one. A negative correlation between ν2 and ν3 and a positive correlation between ν2 and ν4, for all studied collision systems and over full multiplicity range, is observed. The correlation strength computed as symmetric cumulants normalized by the 〈νn2〉 is similar for all collision systems and weakly depends on multiplicity. These measurements provide new evidence for long-range multi-particle collectivity in small collision systems and quantify the nature of its event-by-event fluctuations.