Importance of non-flow in mixed-harmonic multi-particle correlations in small collision systems
Abstract
Recently CMS Collaboration measured mixed-harmonic four-particle azimuthal correlations, known as symmetric cumulants SC (n , m), in pp and p+Pb collisions, and interpreted the non-zero SC (n , m) as evidence for long-range collectivity in these small collision systems. Using the PYTHIA and HIJING models which do not have genuine long-range collectivity, we show that the CMS results, obtained with standard cumulant method, could be dominated by non-flow effects associated with jet and dijets, especially in pp collisions. We show that the non-flow effects are largely suppressed using the recently proposed subevent cumulant methods by requiring azimuthal correlation between two or more pseudorapidity ranges. We argue that the reanalysis of SC (n , m) using the subevent method in experiments is necessary before they can used to provide further evidences for a long-range multi-particle collectivity and constraints on theoretical models in small collision systems.
- Publication:
-
Physics Letters B
- Pub Date:
- February 2018
- DOI:
- 10.1016/j.physletb.2017.12.035
- arXiv:
- arXiv:1710.07567
- Bibcode:
- 2018PhLB..777..201H
- Keywords:
-
- Nuclear Experiment;
- High Energy Physics - Phenomenology;
- Nuclear Theory
- E-Print:
- 7 pages and 6 figures, replace with published version