The collectivity of transverse momentum fluctuations

Abstract

We study the observable $v_0(p_T)$, which quantifies the relative change of $p_T$ spectra induced by event-by-event density fluctuations in the medium created in heavy-ion collisions. This quantity provides a direct measure of radial flow and serves as a probe of collectivity, complementing anisotropic flow coefficients. Using hydrodynamic model calculations, we predict the behavior of $v_0(p_T)$ and show that the scaled quantity $v_0(p_T)/v_0$ exhibits very little dependence on centrality and transport coefficients. We further find that the apparent influence of transport coefficients$-$particularly bulk viscosity$-$ on $v_0(p_T)$ largely originates from modifications of the event-averaged mean transverse momentum, $⟨p_T⟩$. By expressing $v_0(p_T)/v_0$ as a function of $p_T/⟨p_T⟩$, the genuine sensitivity of $v_0(p_T)$ to transport coefficients can be isolated. Moreover, since $v_0(p_T)$ is the $p_T$-differential measure of event-by-event $[p_T]$ fluctuations, it naturally explains the observed $p_T$-cut dependence of ${\sigma }_{p_T}$ measured by ATLAS collaboration.

arXiv comment4 pages, 3 figures, proceedings for Quark Matter 2025 conference, with Acknowledgement

References in corpus (6)

• Measurement of the azimuthal anisotropy of charged particles produced in $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV Pb+Pb collisions with the ATLAS detector
• Transverse momentum fluctuations and their correlation with elliptic flow in nuclear collision
• Measurement of flow harmonics correlations with mean transverse momentum in lead-lead and proton-lead collisions at $\sqrt{s_{NN}}=5.02$ TeV with the ATLAS detector
• Transverse momentum fluctuations in ultrarelativistic Pb+Pb and p+Pb collisions with wounded quarks
• Anisotropic flow and flow fluctuations of identified hadrons in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV
• Disentangling sources of momentum fluctuations in Xe+Xe and Pb+Pb collisions with the ATLAS detector