Non-flow effects in correlation between harmonic flow and transverse momentum in nuclear collisions
Abstract
A large anti-correlation signal between elliptic flow v2 and average transverse momentum [pT ] was recently measured in small collision systems, consistent with a final-state hydrodynamic response to the initial geometry. This negative v2- [pT ] correlation was predicted to change to positive correlation for events with very small charged particle multiplicity Nch due to initial-state momentum anisotropies of the gluon saturation effects. However, the role of non-flow correlations is expected to be important in these systems, which is not yet studied. We estimate the non-flow effects in pp, pPb and peripheral PbPb collisions using Pythia and Hijing models, and compare them with the experimental data. We show that the non-flow effects are largely suppressed using the rapidity-separated subevent cumulant method (details of the cumulant framework are also provided). The magnitude of the residual non-flow is much less than the experimental observation in the higher Nch region, supporting the final-state response interpretation. In the very low Nch region, however, the sign and magnitude of the residual non-flow depend on the model details. Therefore, it is unclear at this moment whether the sign change of v2- [pT ] 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
- E-Print:
- 9 pages, 8 figures including an appendix, replace with published version