Event-by-event investigation of the two-particle source function in $\sqrt{s_{_{\text{NN}}}}=2.76$ TeV PbPb collisions with EPOS

TL;DR

This paper investigates the event-by-event two-particle source functions in PbPb collisions at 2.76 TeV using the EPOS model, revealing Levy-shaped sources with mass-dependent exponents and scaling behaviors consistent with hydrodynamic predictions.

Contribution

It provides the first event-by-event analysis of two-particle source functions in heavy-ion collisions, demonstrating Levy source shapes and their dependence on particle type and collision centrality.

Findings

Levy source shape observed for pions, kaons, and protons.

Lévy scale parameter scales with transverse mass as predicted by hydrodynamics.

Decay products and rescattering influence the source shape and Lévy exponent.

Abstract

The investigation of the two-particle source function in lead-lead collisions simulated by the EPOS model at a center of mass energy per nucleon pair of $\sqrt{s_{_{\text{NN}}}}=2.76$ TeV is presented. The two-particle source functions are reconstructed directly on an event-by-event basis for pions, kaons and protons separately, using the final stage of EPOS. A L\'evy source shape is observed for all three particle species in the individual events, deviating significantly from a Gaussian shape. The source parameters are extracted as functions of collision centrality and pair average transverse mass ($m_{\text{T}}$). The L\'evy exponent is found to be ordered accordingly to particle mass. The L\'evy scale parameter is found to scale for all particle species with $m_{\text{T}}$ according to Gaussian hydrodynamical predictions; however, there is no $m_{\text{T}}$-scaling found across these species. In case of pions, the effects of the decay products and hadronic rescattering are also investigated. The L\'evy exponent is decreased when decay products are also included in the analysis. Without hadronic rescattering and decay products, the source shape is close to a Gaussian.