Nonflow Subtraction Beyond Two-Particle Correlations
Abstract
Establishing collective flow in small collision systems is a crucial and necessary condition for pinning down the minimum conditions for quark-gluon plasma (QGP) formation. In two-particle correlations, nonflow has been subtracted with good control, pushing the reach of flow measurements down to very small event particle multiplicity N. However, the multi-particle nature of collectivity has not been established in the same N regime, because the residual nonflow surviving the subevent procedure in multi-particle cumulants has never been quantified. We develop a general nonflow subtraction framework for m-particle cumulants, built around the approximate 1/Nm−1 scaling of nonflow in the independent-source picture. Correlators containing v1 serve as nonflow-dominated estimators, since the pT-integrated dipolar flow is expected to be small. Using HIJING as a controlled nonflow-only environment, we test the subtraction for three target observables (⟨ v22⟩, ⟨ v22δpT⟩, and c2{4}) in O+O at √(sNN) = 5.36 TeV and 200 GeV and in d+Au at √(sNN) = 200 GeV. Most of the nonflow is removed, with residual fractions typically within 20-30% when converted to the two-particle level, though the best estimator differs across the three targets. We identify a multiplicity-reweighting correction, previously overlooked in two-particle correlations, that explains the long-standing undersubtraction of the naive 1/N-scaling method; its impact grows as a power of the correlator order. The framework gives a systematic route to nonflow subtraction beyond two-particle correlations, broadening the class of multi-particle observables accessible to the small-system flow program.
Versions
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BibTeX
@misc{wang2026nonflow,
title = {{Nonflow Subtraction Beyond Two-Particle Correlations}},
author = {Zaining Wang and Jiangyong Jia and Jinhui Chen and Shengli Huang and Chunjian Zhang and Zhengxi Yan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.10258},
eprint = {2606.10258},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.10258},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Nonflow Subtraction Beyond Two-Particle Correlations
AU - Zaining Wang
AU - Jiangyong Jia
AU - Jinhui Chen
AU - Shengli Huang
AU - Chunjian Zhang
AU - Zhengxi Yan
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2606.10258
UR - https://arxiv.org/abs/2606.10258
AB - Establishing collective flow in small collision systems is a crucial and necessary condition for pinning down the minimum conditions for quark-gluon plasma (QGP) formation. In two-particle correlations, nonflow has been subtracted with good control, pushing the reach of flow measurements down to very small event particle multiplicity N. However, the multi-particle nature of collectivity has not been established in the same N regime, because the residual nonflow surviving the subevent procedure in multi-particle cumulants has never been quantified. We develop a general nonflow subtraction framework for m-particle cumulants, built around the approximate 1/N^m−1 scaling of nonflow in the independent-source picture. Correlators containing v_1 serve as nonflow-dominated estimators, since the p_T-integrated dipolar flow is expected to be small. Using HIJING as a controlled nonflow-only environment, we test the subtraction for three target observables (⟨ v_2^2⟩, ⟨ v_2^2δp_T⟩, and c_2{4}) in O+O at √(s_NN) = 5.36 TeV and 200 GeV and in d+Au at √(s_NN) = 200 GeV. Most of the nonflow is removed, with residual fractions typically within 20-30% when converted to the two-particle level, though the best estimator differs across the three targets. We identify a multiplicity-reweighting correction, previously overlooked in two-particle correlations, that explains the long-standing undersubtraction of the naive 1/N-scaling method; its impact grows as a power of the correlator order. The framework gives a systematic route to nonflow subtraction beyond two-particle correlations, broadening the class of multi-particle observables accessible to the small-system flow program.
ER -