EPJ Featured Talk: First direct measurement of radial flow in heavy-ion collisions with ALICE

TL;DR

This paper reports the first direct measurement of radial flow in heavy-ion collisions using the ALICE detector, revealing mass ordering at low transverse momentum and particle-type differences at higher momentum.

Contribution

It introduces a novel observable, $v_{0}(p_T)$, as a sensitive probe of radial expansion and hadronization in quark-gluon plasma collisions.

Findings

Mass ordering of $v_{0}(p_T)$ at low $p_T$ aligns with hydrodynamics.

Protons show larger $v_{0}(p_T)$ than pions and kaons at high $p_T$, supporting quark recombination.

Results demonstrate $v_{0}(p_T)$'s sensitivity to collective flow and hadronization.

Abstract

This work presents measurements of the transverse-momentum-dependent observable $v_{0}(p_\mathrm{T})$ as a novel probe of radial expansion dynamics in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV with the ALICE detector. Results are reported for inclusive charged hadrons, pions, kaons, and protons across centrality intervals, using a pseudorapidity gap to suppress short-range nonflow correlations. At low $p_\mathrm{T}$, a clear mass ordering is observed, consistent with hydrodynamic expectations. For $p_\mathrm{T} > 3$ GeV/$c$, protons exhibit larger $v_{0}(p_\mathrm{T})$ than pions and kaons, in line with quark recombination models. These results demonstrate the sensitivity of $v_{0}(p_\mathrm{T})$ to collective expansion and hadronization dynamics in the quark--gluon plasma.