Measurement of the flow harmonics correlation 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 $ν_2$ and $v_3$ and a positive correlation between $ν_2$ and $ν_4$, for all studied collision systems and over full multiplicity range, is observed. The correlation strength computed as symmetric cumulants normalized by the $\langle\nu_n^2\rangle$ 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