Space-time regions of high baryon density and baryon stopping in heavy-ion collisions

Abstract

Four-volumes ($V_4=$ spatial-3-volume$\times$lifetime) are calculated within the model of three-fluid dynamics (3FD) and compared with those of the the JET AA Microscopic Transport Model (JAM). The calculations are performed for central Au+Au collisions at energies $\sqrt{s_{NN}}=$ 3 -- 19.6 GeV. These $V_4$ indicate optimal collision-energy ranges for realizing macroscopic high baryon-density matter. It is found that the 3FD four-volumes noticeably exceed those in the JAM, which indicates a stronger baryon stopping in the 3FD model as compared to that JAM. It is argued that this difference in the baryon stopping correlates with stiffness of the EoS implemented in these models. Contrary to JAM, the four-volume, where a baryon density ($n_B$) exceeds three times the normal nuclear density ($n_0$), does not exhibit a maximum as a function of $\sqrt{s_{NN}}$. It decreases monotonically with increasing $\sqrt{s_{NN}}$, remaining at a fairly macroscopic level (i.e. $V_4\geq 5.5^4$ fm$^4$/c). For higher baryon densities, $V_4$ exhibits maxima in its dependence on $\sqrt{s_{NN}}$. The optimal energy range for densities $n_B/n_0>$ 4 is located at $\sqrt{s_{NN}}=$ 3.2--8 GeV. Even for $n_B/n_0>$ 6, the four-volume remains quite macroscopic ($V_4\geq 4^4$ fm$^4$/c) at $\sqrt{s_{NN}}=$ 4.5--9 GeV contrary to the JAM.

Figures (4)

• Figure 1: Time evolution of baryon density in the central region of central ($b$ = 2 fm) Au+Au collisions at various collision energies ($\sqrt{s_{NN}}$) Results for the crossover and 1PT EoSs are displayed. Star symbols on the curves mark the time instant of the baryon-matter stopping.
• Figure 2: Four-volume, in which the baryon density exceeds value $3n_0$ in the central ($b$ = 2 fm) Au+Au collisions as function of collision energy $\sqrt{s_{NN}}$. Calculations are done with the crossover and 1PT EoSs.
• Figure 3: The same as in Fig. \ref{['fig:V4_sNN_3nB_lin']} but separately for equilibrated and non-equilibrated baryon densities.
• Figure 4: Four-volume, in which the baryon density of the equilibrated matter exceeds value $\widetilde{n}_B$ in the central ($b$ = 2 fm) Au+Au collisions, as function of collision energy $\sqrt{s_{NN}}$. Calculations are done with the crossover and 1PT EoSs. The 3FD results are compared with those of JAM Taya:2024zpv of the cascade and mean-field (MF) versions, where all matter (not necessarily equilibrated) was taken into account.