Three-Dimensional two-pion source image from Pb+Pb Collisions at Sqrts_NN=17.3 GeV: New constraints for source breakup dynamics

TL;DR

This study reconstructs a three-dimensional two-pion source function in Pb+Pb collisions at 17.3 GeV, revealing non-Gaussian tails that inform about the source's breakup and emission dynamics.

Contribution

It introduces a source imaging method to analyze pion pairs, providing new constraints on the space-time evolution of the collision source at SPS energies.

Findings

Non-Gaussian tails observed in source function

Model reproduces tails with blast-wave and boost invariance assumptions

Provides estimates for breakup time and emission duration

Abstract

Source imaging methodology is used to provide a three-dimensional two-pion source function for mid-rapidity pion pairs with $p_T<70$ MeV/c in central ($0-7%$) Pb+Pb collisions at $\sqrt s_{NN}$=17.3 GeV. Prominent non-Gaussian tails are observed in the pion pair transverse momentum (outward) and in the beam (longitudinal) directions. Model calculations reproduce them with the assumption of Bjorken longitudinal boost invariance and transverse flow blast-wave dynamics coupled with "outside-in burning" in the transverse direction; they also yield a proper time for breakup and emission duration for the pion source.