Speaker
Description
Event-by-event mean transverse momentum ($p_{\rm T}$) fluctuations provide insight into the initial-state geometry fluctuations, the thermodynamic properties, and the collective evolution of hot and dense QCD matter. In this talk, we will present STAR measurements of event-by-event mean $p_{\rm T}$ fluctuations in Au+Au collisions from the Beam Energy Scan programs, covering collider-mode as well as fixed-target data down to $\sqrt{s_{NN}}=3.0$ GeV. The analysis focuses on the centrality and collision-energy dependence of transverse-momentum correlations and higher moments of the event-by-event mean-$p_{\rm T}$ distribution, including variance, skewness, and kurtosis. The centrality dependence of the multi-particle $p_{\rm T}$ correlations is compared with the expected independent-source scaling behavior, and approximately follows a power-law dependence on the number of participating nucleons. The collision-energy dependence is studied over $\sqrt{s_{NN}}=$3.2--54.4 GeV, and exhibits a non-monotonic behavior, with the most pronounced variation observed in central collisions in the intermediate-energy region. These results are discussed in connection with temperature fluctuations, the QCD equation of state, and possible critical dynamics, with comparisons to LEFT-fRG [1], PNJL [2], and AMPT model calculations [3]. The measurements provide valuable constraints on critical fluctuations and the thermodynamic properties of strongly interacting QCD matter at high baryon density.
References
[1] J. Chen, W.-j. Fu, S. Yin, and C. Zhang, High-Order Fluctuations of Temperature in Hot QCD Matter, Physical Review D 114,014064 (2026).
[2] H. Liu, P. Wu, H.-M. Liu, and P.-C. Chu, Temperature Fluctuations in a Realistic Polyakov-Loop Extended Nambu--Jona-Lasinio Model along the Freeze-Out Line, arXiv:2607.19275 [nucl-th] (2026).
[3] Zhang, Liuyao and Chen, Jinhui and Zhang, Chunjian, Energy dependence of transverse momentum fluctuations in $\mathrm{Au}+\mathrm{Au}$ collisions from a multiphase transport model, Phys. Rev. C 111,024911 (2025).
