Speaker
Description
Radial flow is conventionally studied through transverse-momentum ($p_{T}$) spectra and blast-wave model analyses, which provide information on the average collective expansion and kinetic freeze-out properties of the system. In contrast to the extensively studied anisotropic-flow coefficients $v_{2}$ and $v_{3}$, the $p_{T}$-differential fluctuations of radial flow remain largely unexplored. The recently proposed observable $v_{0}(p_{T})$ provides direct sensitivity to $p_{T}$-differential radial-flow fluctuations~\cite{Schenke_v0,Tribhuban_v0}. The RHIC Beam Energy Scan provides a unique opportunity to investigate how $p_{T}$-differential radial expansion and its event-by-event fluctuations evolve across a broad region of the QCD phase diagram.
In this work, we present measurements of $v_{0}(p_{T})$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7--200 GeV with the STAR experiment at RHIC. The beam-energy and centrality dependence of $v_{0}(p_{T})$ is studied for charged hadrons as well as identified pions, kaons, and protons.Particular emphasis is placed on the slope of the $p_{T}$ dependence of $v_{0}(p_{T})$ and the characteristic $p_{T}$ at which $v_{0}(p_{T})$ changes sign, as these features are sensitive to the strength and fluctuations of radial flow~\cite{Model_v0}. A blast-wave model incorporating event-by-event fluctuations is simultaneously fitted to the proton, kaon, and pion $v_{0}(p_{T})$ data to extract the radial-flow velocity, kinetic freeze-out temperature ($T_{\mathrm{kin}}$), and their event-by-event fluctuations. The extracted parameters provide a quantitative characterization of the beam-energy evolution of the average radial expansion and kinetic freeze-out conditions, as well as their fluctuations, thereby enabling us to assess the relative contributions of radial-flow and freeze-out fluctuations to the observed $v_{0}(p_{T})$ behavior.
\begin{thebibliography}{99}
\bibitem{Schenke_v0}
Björn Schenke, Chun Shen, and Derek Teaney. \textit{Phys. Rev. C 102} (2020), p. 034905.
\bibitem{Tribhuban_v0}
Tribhuban Parida, Rupam Samanta, and Jean-Yves Ollitrault. \textit{Phys. Lett. B 857} (2024), p. 138985.
\bibitem{Model_v0}
Syed Afrid Jahan, Hendrik Roch, and Chun Shen. arXiv:2507.11394 (2025).
\end{thebibliography}
