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.

arXiv comment7 pages and 6 figures, replace with published version

References in corpus (17)

• A Brief Introduction to PYTHIA 8.1
• HIJING 1.0: A Monte Carlo Program for Parton and Particle Production in High Energy Hadronic and Nuclear Collisions
• Long-range angular correlations on the near and away side in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV
• Observation of long-range near-side angular correlations in proton-lead collisions at the LHC
• Observation of Associated Near-side and Away-side Long-range Correlations in sqrt(s_NN)=5.02 TeV Proton-lead Collisions with the ATLAS Detector
• Flow analysis with cumulants: direct calculations
• Evidence for collectivity in pp collisions at the LHC
• Flow analysis from multiparticle azimuthal correlations
• Observation of long-range elliptic anisotropies in $\sqrt{s}=$13 and 2.76 TeV $pp$ collisions with the ATLAS detector
• New method for measuring azimuthal distributions in nucleus-nucleus collisions
• Comparison of the Color Glass Condensate to di-hadron correlations in proton-proton and proton-nucleus collisions
• Evidence for collective multi-particle correlations in pPb collisions
• Generic framework for anisotropic flow analyses with multi-particle azimuthal correlations
• Collective dynamics of the high-energy proton-nucleus collisions
• Measurement of multi-particle azimuthal correlations in $pp$, $p$+Pb and low-multiplicity Pb+Pb collisions with the ATLAS detector
• Revealing long-range multi-particle collectivity in small collision systems via subevent cumulants
• Measurements of long-range azimuthal anisotropies and associated Fourier coefficients for $pp$ collisions at $\sqrt{s}=5.02$ and $13$ TeV and $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ATLAS detector

Cited by in corpus (34)

• The ALICE experiment: a journey through QCD
• Anisotropic flow in Xe-Xe collisions at $\sqrt{{\mathbf{s}}_{\mathrm{NN}}}=5.44$ TeV
• Investigations of anisotropic flow using multi-particle azimuthal correlations in pp, p-Pb, Xe-Xe, and Pb-Pb collisions at the LHC
• Hydrodynamic Collectivity in Proton--Proton Collisions at 13 TeV
• Shrinking the Quark Gluon Plasma
• Multi-particle and charge-dependent azimuthal correlations in heavy-ion collisions at the Relativistic Heavy-Ion Collider
• Correlated long-range mixed-harmonic fluctuations measured in $pp$, $p$+Pb and low-multiplicity Pb+Pb collisions with the ATLAS detector
• Fluctuations of anisotropic flow in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with the ATLAS detector
• Correlations between flow and transverse momentum in Xe+Xe and Pb+Pb collisions at the LHC with the ATLAS detector: a probe of the heavy-ion initial state and nuclear deformation
• Centrality fluctuations in heavy-ion collisions
• Generic algorithm for multi-particle cumulants of azimuthal correlations in high energy nucleus collisions
• Progress and Challenges in Small Systems
• Anisotropic flow and flow fluctuations of identified hadrons in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV
• Multiparticle azimuthal cumulants in p+Pb collisions from a multiphase transport model
• Higher-order transverse momentum fluctuations in heavy-ion collisions
• Non-flow effects in correlation between harmonic flow and transverse momentum in nuclear collisions
• Probe nuclear structure using the anisotropic flow at the Large Hadron Collider
• Non-flow effects in three-particle mixed-harmonic azimuthal correlations in small collision systems
• Model investigations of the correlation between the mean transverse momentum and anisotropic flow in shape-engineered events
• Characterizing the initial and final state effects of relativistic nuclear collisions
• Measuring differential flow angle fluctuations in relativistic nuclear collisions
• ALICE measurements of flow coefficients and their correlations in small (pp and p-Pb) and large (Xe-Xe and Pb-Pb) collision systems
• Correlations of azimuthal anisotropy Fourier harmonics with subevent cumulants in pPb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 8.16 TeV
• Model study of the energy dependence of the correlation between anisotropic flow and the mean transverse momentum in Au+Au collisions
• Exploring nuclear structure with multiparticle azimuthal correlations at the LHC
• Azimuthal anisotropies of charged particles with high transverse momentum in Pb+Pb collisions at $\sqrt{s_{{}_{\text{NN}}}}=5.02$ TeV with the ATLAS detector
• Pseudorapidity dependence of anisotropic flow and its decorrelations using long-range multiparticle correlations in Pb-Pb and Xe-Xe collisions
• Symmetric cumulant $s{c}_{2,4}\left\{4\right\}$ and asymmetric cumulant $a{c}_2\left\{3\right\}$ from transverse momentum conservation and flow
• Measuring differential particle correlations in relativistic nuclear collisions
• Measurements of mixed harmonic cumulants in Pb-Pb collisions at $\sqrt{{\text{s}}_{\mathrm{NN}}}=5.02$ TeV
• Hadronic Rescattering in pA and AA Collisions
• Beam-energy dependence of correlations between mean transverse momentum and anisotropic flow of charged particles in Au+Au collisions at RHIC
• Effect of event classification on the Tsallis-thermometer
• Characterizing the initial conditions of heavy-ion collisions at the LHC with mean transverse momentum and anisotropic flow correlations