Multi-particle azimuthal cumulants in p+Pb collisions from a multiphase transport model.

A new subevent cumulant method was recently developed, which can significantly reduce the non-flow contributions in long-range correlations for small systems. In this work, we use both standard and subevent cumulant methods to study multi-particle correlations in $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV with a multiphase transport (AMPT) model, including two- and four-particle cumulants ($c_{2}\{2\}$ and $c_{2}\{4\}$) and symmetric cumulants (SC(2, 3) and SC(2, 4)). Our numerical results show that $v_{2}\{2\}$ is consistent with the experimental data, while the magnitude of $c_{2}\{4\}$ is smaller than the experimental data, which may indicate either the collectivity is underestimated or some dynamical fluctuations are missed in the AMPT model. For the symmetric cumulants, we find that the results from standard cumulant method are consistent with the recent CMS data, but those from subevent cumulant method show different behaviors. It indicates that the measurements from the standard cumulant method could be contaminated by some non-flow effects, especially when the number of produced particles is small. Our results support the subevent cumulant method to be a better tool to explore the $real$ collectivity in small systems.