Comprehensive modeling of baryon and electric charge transport in heavy-ion collisions

The rapidity distributions of conserved charges—net baryon number, electric charge, and strangeness—in relativistic heavy-ion collisions encode key information about initial-state baryon stopping, the nature of charge carriers such as string junctions, and the nuclear structure of the colliding systems. Using state-of-the-art (3+1)D hydrodynamic simulations coupled with hadronic transport, we provide a quantitative assessment of baryon stopping induced by the baryon junction mechanism. We demonstrate that the enhanced stopping from this mechanism is in quantitative agreement with STAR’s double ratio measurements in isobar collisions [1,2]. In addition, we propose a systematic approach using thermal model calculations to extract baryon stopping, offering a new avenue for quantitative analysis.

Given the sensitivity of these observables to the neutron skin thickness, we introduce novel strategies to constrain the neutron skin based on the longitudinal profiles of conserved charges. In particular, we generalize the STAR double ratio observable and show that the extended definition exhibits a clear dependence on the neutron skin thickness within thermal calculations. This renders the observable a practical and precise experimental probe of neutron density distributions in heavy nuclei.

[1] STAR Collaboration, extit{Tracking the baryon number with nuclear collisions}, arXiv:2408.15441

[2] G. Pihan, A. Monnai, B. Schenke, and C. Shen, extit{Unveiling baryon charge carriers through charge stopping in isobar collision}, Phys. Rev. Lett. 133, 182301