Bayesian extraction of TMC-free collectivity in p+p and p+Pb collisions at the LHC

Abstract

A central challenge in understanding the origin of collective flow-like signatures in small collision systems calls for a reliable method to disentangle genuine collective flow from substantial background correlations, especially those arising from transverse momentum conservation (TMC). A Bayesian inference framework is developed to integrate TMC calculations with the LHC-ATLAS data on long-range multiparticle azimuthal correlation observables, thereby extracting genuine collective flow in small systems. Our analysis indicates that while the genuine elliptic and triangular flow ($v_2$ and $v_3$) are similar, the $p$+$p$ and $p$+Pb systems exhibit distinct TMC backgrounds, TMC-flow interplay, and $v_2$--$v_3$ correlations. We demonstrate that the genuine $v_2$ and $v_3$ are well described by the measured four-particle $v_2\{4\}$ and two-particle $v_3\{2\}$ in $p$+Pb collisions, whereas these measurements systematically underestimate the genuine flow in $p$+$p$ collisions, due to competing contributions from TMC effects. This establishes a robust and data-driven approach, providing renewed theoretical insight into collective behavior free from TMC contamination in small collision systems.

Comments: 14 pages, 6 figures