Vorticity-induced modifications of chemical freeze-out in heavy-ion collisions

Abstract

We investigate the influence of global rotation on the chemical freeze-out parameters in ultra-relativistic heavy-ion collisions. Within the framework of the hadron resonance gas (HRG) model, the freeze-out parameters are determined using commonly employed freeze-out criteria, namely the fixed energy per particle and the scaled entropy density, extended here to include rotational effects. We find that the presence of rotation leads to a systematic shift of the chemical freeze-out curve toward lower temperatures in the $T\text{--}μ_B$ phase diagram. The behavior of the electric charge and strangeness chemical potentials in the presence of rotation is also analyzed, providing the first systematic study of their rotational dependence within the HRG framework. Furthermore, we examine the impact of rotation on experimentally relevant observables, including hadron yield ratios and susceptibility ratios of conserved charges. Our results show that while particle yield ratios exhibit noticeable sensitivity to rotation, the conventional cumulant ratios remain comparatively less affected. This indicates that hadronic yield ratios may provide a more suitable observable for estimating the magnitude of rotational effects generated in heavy-ion collisions.

Figures (8)

• Figure 1: (Colour Online) The freeze-out curve in the $T-\mu_B$ plane is obtained using the conditions of constant average energy per particle, $\langle \varepsilon \rangle/\langle n \rangle = 1.08~\mathrm{GeV}$ (left), and constant entropy density, $s/T^3 = 7$ (right). The results at $\omega = 0$ are compared with those reported by Cleymans et al. Cleymans:2005xv, and are further extended to finite rotation with $\omega = 0.005$, $0.01$, and $0.015~\mathrm{GeV}$.
• Figure 2: (Colour Online) The shift in freeze-out temperature ($\Delta T$) as a function of $\omega$ for $\mu_B = 0.2$ and $0.6$ GeV.
• Figure 3: (Colour Online) The electric charge and Strangeness chemical potential as a function of T and $\mu_B$ for $\omega$ = 0 and 0.015 GeV.
• Figure 4: (Colour Online) The leading-order expansion coefficients of the negative of electric charge (left) and strangeness chemical potentials (right) as a function of temperature at $\mu_B$ = 0 for different magnitudes of rotation.
• Figure 5: (Colour Online) The chemical potentials $\mu_Q$ and $\mu_S$ obtained using two different approaches are compared as a function of $\mu_B$ at $\omega$ = 0 (left) and as a function of $\omega$ at $\mu_B$ = 0.2 GeV and T = 160 MeV (right).