This Letter presents measurements of long-range transverse-momentum correlations using a new observable, $v_{0}(p_\mathrm{T})$, which serves as a probe of radial flow and medium properties in heavy-ion collisions. Results are reported for inclusive charged particles, pions, kaons, and protons across various centrality intervals in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV, recorded by the ALICE detector. A pseudorapidity-gap technique, similar to that used in anisotropic-flow studies, is employed to suppress short-range correlations. At low $p_\mathrm{T}$, a characteristic mass ordering consistent with hydrodynamic collective flow is observed. At higher $p_\mathrm{T}$ ($> 3$ GeV/$c$), protons exhibit larger $v_{0}(p_\mathrm{T})$ than pions and kaons, in agreement with expectations from quark-recombination models. These results are sensitive to the bulk viscosity and the equation of state of the QCD medium formed in heavy-ion collisions.
Submitted to: PRL
e-Print: arXiv:2504.04796 | PDF | inSPIRE
CERN-EP-2025-084
Figure group
Figure 1
$v_{0}(p_\mathrm{T})$ of inclusive charged particles shown as a function of $p_\mathrm{T}$ in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV for centrality intervals 10$-$20\% (top left), 30$-$40\% (top right), and 60$-$70\% (bottom left). The measurements are compared to expectations from HIJING and IP-Glasma+MUSIC+UrQMD models. $v_{0}(p_\mathrm{T})/v_{0}$ of inclusive charged particles shown as a function of $p_\mathrm{T}$ for the centrality intervals (bottom right). The statistical (systematic) uncertainties are represented by vertical bars (boxes). |  |
Figure 2
$v_{0}(p_\mathrm{T})$ of pions ($\pi^{\pm}$), kaons ($\mathrm{K}^{\pm}$), and protons ($\mathrm{p}(\bar{\mathrm{p}})$) shown as a function of $p_\mathrm{T}$ in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV for centrality intervals 10$-$20\% (left), 30$-$40\% (middle), and 60$-$70\% (right). The measurements are compared to results from HIJING and IP-Glasma+MUSIC+UrQMD models. The statistical (systematic) uncertainties are represented by vertical bars (boxes). The bottom panels show the (Data-Model)/$\sigma$, representing the deviation between the experimental data and model predictions, normalized by the uncertainty. |  |
Figure 3
Left: $v_{0}(p_\mathrm{T})$ of inclusive charged particles shown as a function of $p_\mathrm{T}$ for centrality intervals 10$-$20\%, compared to hydrodynamic model predictions from IP-Glasma+MUSIC+UrQMD framework with varying transport coefficients ($\eta/s$ and $\zeta/s$), in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV. Right: same measurements are compared to hydrodynamic model predictions with different equations of state (EOS) from Ref. . The statistical (systematic) uncertainties are represented by vertical bars (boxes). |   |
Figure A.2
$v_{0}(p_\mathrm{T})$ of inclusive charged particles shown as a function of $p_\mathrm{T}$ for centrality intervals 10$-$20\% (left), 30$-$40\% (middle), and 60$-$70\% (right) for varying pseudorapidity gap ($\Delta\eta$) in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV. The error bars represent statistical uncertainties. The bottom panel presents the ratio relative to the results for $\Delta\eta = 0$. |    |
Figure A.3
HIJING model based calculations of $v_{0}(p_\mathrm{T})$ of inclusive charged particles as a function of $p_\mathrm{T}$ for centrality intervals 10$-$20\% (left), 30$-$40\% (middle), and 60$-$70\% (right) in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV. The results at the generated and reconstructed level are shown, with lines connecting the central values and bands representing the statistical uncertainties. |    |
Figure A.4
$v_{0}(p_\mathrm{T})$ of inclusive charged particles shown as a function of $p_\mathrm{T}$ for centrality intervals 10$-$20\% (left), 30$-$40\% (middle), and 60$-$70\% (right) for varying pseudorapidity gap ($\Delta\eta$) and azimuthal acceptance ($\varphi$) in Pb$-$Pb collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV. The statistical (systematic) uncertainties are represented by vertical bars (boxes). The bottom panel presents the ratio relative to the results for $\Delta\eta = 0.4, 0 \varphi 2\pi$. |    |