Speaker
Description
We report the first measurements of two-particle transverse-momentum correlations (variance) for midrapidity charged particles in fixed-target Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=3.0$--$7.7$ GeV using data collected by STAR during the Beam Energy Scan Phase II program [1]. Combined with previous BES-I measurements at $\sqrt{s_{\mathrm{NN}}}=7.7$--$200$ GeV [2], the relative dynamical correlator approximately follows the $1/\sqrt{N_{\mathrm{part}}}$ scaling expected from independent particle-emitting sources at most energies. The scaling breaks down at the lowest collision energy, while additional deviations emerge in central collisions. For 0--5% central collisions, the combined data exhibit a non-monotonic beam-energy dependence with a significance of approximately $5\sigma$ relative to a monotonic baseline. In comparison, the mid-central data and AMPT calculations yield deviations of only approximately $2\sigma$ and $1.4\sigma$, respectively. Possible connections to temperature fluctuations and QCD critical dynamics are discussed using recent $2+1$-flavor LEFT-fRG and PNJL model calculations [3, 4]. The observations provide valuable input to understand the critical fluctuations and new constraints on the equation of state at high baryon density.
References
- STAR Collaboration, "Non-Monotonicity of Transverse Momentum Correlations in Au+Au Collisions at RHIC," arXiv:2604.06434 [nucl-ex] (2026), accepted for publication in Physical Review Letters.
- STAR Collaboration, "Collision Energy Dependence of $p_{\mathrm{T}}$ Correlations in Au+Au Collisions at RHIC," Phys. Rev. C 99, 044918 (2019).
- J. Chen, W.-j. Fu, S. Yin, and C. Zhang, "High-Order Fluctuations of Temperature in Hot QCD Matter," arXiv:2504.06886 [hep-ph] (2025), Phys. Rev. D, 114, 014064 (2026).
- 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).
