2025/12/02 by Huang, Yan, Molnar, Matyas, Kincses, Daniel +1 · 1 citation
#FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #Nuclear Theory (nucl-th)
paper · doi:10.48550/arxiv.2512.02560
Three-dimensional (3D) femtoscopic source parameters of pions provide a sensitive probe of the space-time structure of particle-emitting sources in high-energy heavy-ion collisions. Compared to one-dimensional measurements, 3D femtoscopy not only provides a valuable cross-check but also offers a more complete characterization of the source geometry and its dynamical evolution. Particularly, differences between the "out" and "side" directions are sensitive to signals of a strong first-order phase transition, while the collision-energy dependence of Levy radii may reveal non-monotonic features related to the equation of state (EoS). In this work, we systematically investigate the transverse mass and collision-energy dependence of the three-dimensional femtoscopic parameters of pion pairs with Levy-type sources in the STAR Beam Energy Scan (BES) range from √sNN = 7.7 to 200 GeV using the EPOS4 model. The analyzed parameters include the Levy index α, the correlation strength λ, and the three-dimensional radii R_\rm out, R\rm side and R\rm long , derived quantities such as the radius difference R\rm diff = R\rm out2 - R\rm side2 and the ratio R\rm out/R\rm side are also investigated. The results show that the extracted radii R_\rm side and R\rm long decrease with increasing transverse momentum and increase gradually with collision energy, while R_\rm out shows little energy dependence. The Levy index α exhibits only a mild dependence on mT and collision energy, whereas the correlation strength λ shows a clear mT dependence and generally decreases with increasing collision energy. A comparison with EPOS3 results indicates general agreement within approximately 2σ, with the notable exception of R\rm side, which is systematically smaller in EPOS4.