Speaker
Description
A newly proposed observable, $v_0$, and its transverse-momentum-differential
form, $v_0(p_T)$, is designed to quantify event-by-event variations in the spectral shape
associated with radial-flow fluctuations[1-4]. This observable is sensitive to
the equation of state (EoS) of the medium, and several phenomenological studies have
identified it as a potential signature of partonic collectivity.
STAR measurements of elliptic flow at high baryon density, obtained in Au+Au fixed-target collisions at $\sqrt{s_{NN}}$=3.0--4.5 GeV, indicate that signatures of partonic collectivity weaken across this energy range, suggesting a transition in the EoS from partonic to hadronic dominance[5]. Measuring $v_{0}$ and $v_{0}(p_{T})$ in this energy regime could therefore provide additional constraints on the EoS.
In this presentation, we report the first measurements of $v_{0}$ and $v_{0}(p_{T})$ for identified hadrons in Au+Au fixed-target collisions at $\sqrt{s_{NN}} = 3.0$--$4.5$ GeV using data recorded by the STAR experiment, and discuss the implications for partonic collectivity and the EoS at high baryon density. The results are compared to transport model calculations to gain further insight into the nature of the medium in this energy regime.
[1] B. Schenke, C. Shen, D. Teaney, Phys. Rev. C 102, 034905 (2020).
[2] T. Parida, R. Samanta, J.-Y. Ollitrault, Phys. Lett. B 857, 138985 (2024).
[3] ATLAS Collaboration, Phys. Rev. Lett. 136, 031901 (2026).
[4] ALICE Collaboration, Phys. Rev. Lett. 136, 032302 (2026).
[5] STAR Collaboration, Phys. Rev. Lett. 135, 072301 (2025).
