Femtoscopic parameters of pion emission sources in EPOS4 Au+Au collisions from 7.7 to 200 GeV
Abstract
Three-dimensional femtoscopy probes the space-time structure of particle-emitting sources in relativistic heavy-ion collisions. The collision-energy dependence of Lévy source parameters may reveal the evolution of strongly interacting matter and possible signatures of the QCD phase diagram. We previously studied the excitation function of three-dimensional Lévy source parameters for pion pairs in Au+Au collisions with EPOS4, analyzing the pair-distance distribution D(ρ) through one-dimensional projections. Here, we analyze the full three-dimensional source distribution and correlation function directly. We construct D(ρout,ρside,ρlong) as a 3D histogram, transform it into C(qout,qside,qlong) using a Fast Fourier Transform, and fit the correlation function with the analytic Lévy formula. This approach can reduce biases arising when one-dimensional projections are used to describe a non-elliptical source. We apply the method across the RHIC Beam Energy Scan range and compare the extracted energy dependence with results from the projection-based method and recent UrQMD calculations. We focus on the out-side observables Rdiff2=Rout2−Rside2 and Rout/Rside, whose different energy dependences in EPOS4 and UrQMD may illuminate the roles of emission duration and source dynamics. This work establishes a direct three-dimensional framework for comparison with future femtoscopic measurements and for exploring possible non-monotonic structures associated with the QCD phase diagram.
Related
- Lévy-stable pion emission sources in Au+Au collisions at √(sNN)=200 GeV from the vHLLE+SMASH hybrid model
- Nuclear Geometry-Driven Femtoscopic Correlations in Light-Ion Collisions
- Levy-shaped femtoscopic sources from an exact solution of relativistic hydrodynamics
- Separating entanglement at emission from femtoscopic correlations
- Simulating the emission source function in very peripheral relativistic heavy-ion collisions
BibTeX
@misc{huang2026femtoscopic,
title = {{Femtoscopic parameters of pion emission sources in EPOS4 Au+Au collisions from 7.7 to 200 GeV}},
author = {Yan Huang and Máté Csanád},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.18257},
eprint = {2610.18257},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.18257},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Femtoscopic parameters of pion emission sources in EPOS4 Au+Au collisions from 7.7 to 200 GeV
AU - Yan Huang
AU - Máté Csanád
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.18257
UR - https://arxiv.org/abs/2610.18257
AB - Three-dimensional femtoscopy probes the space-time structure of particle-emitting sources in relativistic heavy-ion collisions. The collision-energy dependence of Lévy source parameters may reveal the evolution of strongly interacting matter and possible signatures of the QCD phase diagram. We previously studied the excitation function of three-dimensional Lévy source parameters for pion pairs in Au+Au collisions with EPOS4, analyzing the pair-distance distribution D(ρ) through one-dimensional projections. Here, we analyze the full three-dimensional source distribution and correlation function directly. We construct D(ρ_out,ρ_side,ρ_long) as a 3D histogram, transform it into C(q_out,q_side,q_long) using a Fast Fourier Transform, and fit the correlation function with the analytic Lévy formula. This approach can reduce biases arising when one-dimensional projections are used to describe a non-elliptical source. We apply the method across the RHIC Beam Energy Scan range and compare the extracted energy dependence with results from the projection-based method and recent UrQMD calculations. We focus on the out-side observables R_diff^2=R_out^2−R_side^2 and R_out/R_side, whose different energy dependences in EPOS4 and UrQMD may illuminate the roles of emission duration and source dynamics. This work establishes a direct three-dimensional framework for comparison with future femtoscopic measurements and for exploring possible non-monotonic structures associated with the QCD phase diagram.
ER -