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 pPb 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.

7 pages and 6 figures, replace with published version

References in corpus (2)

• Observation of long-range near-side angular correlations in proton-lead collisions at the LHC
• Evidence for collective multi-particle correlations in pPb collisions

Cited by in corpus (22)

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• Characterizing the initial and final state effects of relativistic nuclear collisions
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• Pseudorapidity dependence of anisotropic flow and its decorrelations using long-range multiparticle correlations in Pb-Pb and Xe-Xe collisions
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• Measurements of mixed harmonic cumulants in Pb-Pb collisions at $\sqrt{{\text{s}}_{\mathrm{NN}}}=5.02$ TeV
• Characterizing the initial conditions of heavy-ion collisions at the LHC with mean transverse momentum and anisotropic flow correlations
• Hadronic Rescattering in pA and AA Collisions
• Effect of event classification on the Tsallis-thermometer
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