Nonflow effects in correlation between harmonic flow and transverse momentum in nuclear collisions
Abstract
A large anticorrelation signal between elliptic flow v_{2} and average transverse momentum [p_{T} ] was recently measured in small collision systems, consistent with a finalstate hydrodynamic response to the initial geometry. This negative v_{2} [p_{T} ] correlation was predicted to change to positive correlation for events with very small charged particle multiplicity N_{ch} due to initialstate momentum anisotropies of the gluon saturation effects. However, the role of nonflow correlations is expected to be important in these systems, which is not yet studied. We estimate the nonflow effects in pp, pPb and peripheral PbPb collisions using Pythia and Hijing models, and compare them with the experimental data. We show that the nonflow effects are largely suppressed using the rapidityseparated subevent cumulant method (details of the cumulant framework are also provided). The magnitude of the residual nonflow is much less than the experimental observation in the higher N_{ch} region, supporting the finalstate response interpretation. In the very low N_{ch} region, however, the sign and magnitude of the residual nonflow depend on the model details. Therefore, it is unclear at this moment whether the sign change of v_{2} [p_{T} ] can serve as evidence for initial state momentum anisotropies predicted by the gluon saturation.
 Publication:

Physics Letters B
 Pub Date:
 November 2021
 DOI:
 10.1016/j.physletb.2021.136702
 arXiv:
 arXiv:2102.05200
 Bibcode:
 2021PhLB..82236702Z
 Keywords:

 Nuclear Theory;
 High Energy Physics  Phenomenology;
 Nuclear Experiment
 EPrint:
 9 pages, 8 figures including an appendix, replace with published version