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Title: Revealing long-range multiparticle collectivity in small collision systems via subevent cumulants

Abstract

Multi-particle azimuthal cumulants, often used to study collective flow in high-energy heavy-ion collisions, have recently been applied in small collision systems such as pp and p+A to extract the second-order azimuthal harmonic flow v 2. Recent observation of four-, six- and eight-particle cumulants with “correct sign” c 2{4} < 0, c 2{6} > 0, c 2{8} < 0 and approximate equality of the inferred single-particle harmonic flow, v 2{4} ≈ v 2{6} ≈ v 2{8}, have been used as strong evidence for a collective emission of all soft particles produced in the collisions. In this paper, we show that these relations in principle could be violated due to the non-Gaussianity in the event-by-event fluctuation of flow and/or non-flow. Furthermore, we show, using pp events generated with the PYTHIA model, that c 2{2k} obtained with standard cumulant method are dominated by non-flow from dijets. An alternative cumulant method based on two or more η-separated subevents is proposed to suppress the dijet contribution. The new method is shown to be able to recover a flow signal as low as 4% imposed on the PYTHIA events, independently of how the event activity class is defined. Therefore the subevent cumulant method offers a moremore » robust way of studying collectivity based on the existence of long-range azimuthal correlations between multiple distinct η ranges. Finally, the prospect of using the subevent cumulants to study collective flow in A+A collisions, in particular its longitudinal dynamics, is discussed.« less

Authors:
 [1];  [2];  [3]
  1. Stony Brook Univ., NY (United States). Department of Chemistry; Brookhaven National Lab. (BNL), Upton, NY (United States). Physics Department
  2. Stony Brook Univ., NY (United States). Department of Chemistry
  3. Polish Academy of Sciences, Krakow (Poland). Institute of Nuclear Physics
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
OSTI Identifier:
1430890
Report Number(s):
BNL-203404-2018-JAAM
Journal ID: ISSN 2469-9985; PRVCAN; TRN: US1802926
Grant/Contract Number:  
SC0012704
Resource Type:
Accepted Manuscript
Journal Name:
Physical Review C
Additional Journal Information:
Journal Volume: 96; Journal Issue: 3; Journal ID: ISSN 2469-9985
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS

Citation Formats

Jia, Jiangyong, Zhou, Mingliang, and Trzupek, Adam. Revealing long-range multiparticle collectivity in small collision systems via subevent cumulants. United States: N. p., 2017. Web. doi:10.1103/PhysRevC.96.034906.
Jia, Jiangyong, Zhou, Mingliang, & Trzupek, Adam. Revealing long-range multiparticle collectivity in small collision systems via subevent cumulants. United States. doi:10.1103/PhysRevC.96.034906.
Jia, Jiangyong, Zhou, Mingliang, and Trzupek, Adam. Mon . "Revealing long-range multiparticle collectivity in small collision systems via subevent cumulants". United States. doi:10.1103/PhysRevC.96.034906. https://www.osti.gov/servlets/purl/1430890.
@article{osti_1430890,
title = {Revealing long-range multiparticle collectivity in small collision systems via subevent cumulants},
author = {Jia, Jiangyong and Zhou, Mingliang and Trzupek, Adam},
abstractNote = {Multi-particle azimuthal cumulants, often used to study collective flow in high-energy heavy-ion collisions, have recently been applied in small collision systems such as pp and p+A to extract the second-order azimuthal harmonic flow v2. Recent observation of four-, six- and eight-particle cumulants with “correct sign” c2{4} < 0, c2{6} > 0, c2{8} < 0 and approximate equality of the inferred single-particle harmonic flow, v2{4} ≈ v2{6} ≈ v2{8}, have been used as strong evidence for a collective emission of all soft particles produced in the collisions. In this paper, we show that these relations in principle could be violated due to the non-Gaussianity in the event-by-event fluctuation of flow and/or non-flow. Furthermore, we show, using pp events generated with the PYTHIA model, that c2{2k} obtained with standard cumulant method are dominated by non-flow from dijets. An alternative cumulant method based on two or more η-separated subevents is proposed to suppress the dijet contribution. The new method is shown to be able to recover a flow signal as low as 4% imposed on the PYTHIA events, independently of how the event activity class is defined. Therefore the subevent cumulant method offers a more robust way of studying collectivity based on the existence of long-range azimuthal correlations between multiple distinct η ranges. Finally, the prospect of using the subevent cumulants to study collective flow in A+A collisions, in particular its longitudinal dynamics, is discussed.},
doi = {10.1103/PhysRevC.96.034906},
journal = {Physical Review C},
number = 3,
volume = 96,
place = {United States},
year = {2017},
month = {9}
}

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