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

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.

Figures (2)

• Figure 1: The distributions of $v_0(p_\mathrm{T})$ for charged particles in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV, shown for central (10--20%), semicentral (30--40%), and peripheral (60--70%) collisions. Comparisons with HIJING (dashed) and IP-Glasma+MUSIC+UrQMD (solid) models are shown. The scaled ratio $v_0(p_\mathrm{T})/v_0$ appears in the bottom right panel. Error bars (boxes) show statistical (systematic) uncertainties.
• Figure 2: The distributions of $v_0(p_\mathrm{T})$ for identified particles ($\pi^\pm$, $K^\pm$, $p/\bar{p}$) in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV, shown for central (10--20%), semicentral (30--40%), and peripheral (60--70%) collisions. Data are compared to HIJING and IP-Glasma+MUSIC+UrQMD predictions. Statistical (systematic) uncertainties appear as vertical bars (boxes). Bottom panels display normalized residuals (Data--Model)/$\sigma$.