Precision Imaging of the Pion Emission Source in Heavy-Ion Collisions via a Global Rest Frame Analysis

TL;DR

The paper addresses frame-dependent distortions in pion imaging within heavy-ion collisions and identifies that conventional CMFP-based imaging introduces a non-Gaussian tail in the reconstructed source $S(r)$. It proposes a CMFS-based correlation analysis, employing selective energy-difference filtering to minimize the perturbation $| riangle E|$ and using model-independent imaging to extract $S(r)$ in the physically meaningful rest frame. Validation against Gaussian-model sources and AMPT simulations shows that CMFS imaging suppresses the artificial tail and recovers the true source morphology with higher fidelity. This approach provides a clearer probe of the spacetime structure of the collision fireball and can be applied to existing and future data to improve insights into emission geometry and long-range correlations $S(r)$.

Abstract

Conventional imaging of pion emission sources, conducted in the center-of-mass frame of individual pion pairs (CMFP), suffers from frame-dependent kinematic distortions that bias the reconstructed source morphology. This method introduces spurious correlations due to the relative boost between the CMFP and the true source rest frame (CMFS), leading to systematic image distortions with a pronounced non-Gaussian tail. We present a transformative approach by performing correlation analysis directly in the global source rest frame (CMFS), the physically meaningful reference frame of the collision fireball. This paradigm shift eliminates kinematic contamination inherent in conventional CMFP-based imaging. The resulting source image shows a dramatic suppression of the non-Gaussian artifact and achieves significantly better agreement with pristine model source functions. Our technique offers a more direct and uncontaminated probe of the intrinsic source geometry, overcoming the limitations of prior methods. It provides a clearer and more accurate determination of the spacetime properties of the nuclear collision fireball, marking a significant advancement in the field.

Figures (3)

• Figure 1: (color online). The comparison between the model source(solid curve) and the imaging source($\blacksquare$) with a Gaussian model in the CMFP. A Gaussian curve($\blacktriangle$) is added to check the result.
• Figure 2: (color online). The comparison between the model source(solid curve) and the imaging source($\blacksquare$) with a Gaussian model in the CMFS. A Gaussian curve($\blacktriangle$) is added to check the result.
• Figure 3: (color online). Comparison of effects of long tail between the results in the CMFP(a) and CMFS(b) with the AMPT model.