Speaker
Description
Event-by-event mean transverse momentum fluctuations (⟨pT⟩) provide a sensitive probe of the initial-state energy-geometry and transverse-size fluctuations and their conversion into collective dynamics in relativistic heavy-ion collisions. We present a systematic study of second-order mean-pT fluctuations in Au+Au collisions at √sNN = 3.0–19.6 GeV using the updated Jet AA Microscopic Transport Model, JAM2. The calculations are performed in the RQMDv mode of JAM2, in which Skyrme-type density- and momentum-dependent hadronic mean fields are implemented as Lorentz-vector potentials to describe pressure-driven dynamics in baryon-rich matter. Comparisons withmeasured identified-particle pT spectra and inclusive ⟨pT⟩ measurements at RHIC BES energies
establish a reasonable baseline for the bulk transverse-momentum evolution. The scaled second-order pT correlator decreases approximately as a power-law behavior with increasing number of participating nucleons. JAM2 reasonably describes the magnitude and centrality dependence of the available STAR measurements at √sNN = 7.7–19.6 GeV, but predicts a steeper centrality dependence at 3.0–4.5 GeV. The identified-particle analysis reveals substantially larger positive correlations for protons and antiprotons than for charged pions, indicating a stronger baryon sensitivity to radical flow and high-density mean-field dynamics. The pion two-particle correlator, ⟨c2⟩, is negative or consistent with zero over most centralities at √sNN = 3.0 and 3.5 GeV, becomes weakly positive at 4.5 GeV, and remains positive with little beam-energy dependence for √sNN ≥ 7.7 GeV. This evolution qualitatively parallels that calculated elliptic flow, which changes from low-energy squeeze-out to in-plane expansion at higher energies. These results provide a JAM2 transport baseline for
interpreting ⟨pT⟩ fluctuations in the baryon-rich region explored by the RHIC BES and future low-energy heavy-ion programs at HIRFL and HIAF
