Entropy in the nuclear caloric curve

Experimental studies have obtained the caloric curve of nuclear matter from heavy ion collisions and studied its size dependence. This work investigates the thermodynamics of a heavy ion collision and concludes that the plateau temperature of the caloric curve is determined by the entropy generated during the initial part of the collision, which in turn is related to the size of the system.

Figure 1

Possible trajectory of a heavy ion collision plotted on the phase diagram of Ref. 20. The solid semicircle represents the boundary of the phase coexistence region, the dashed line is the spinodal line, and the traverse line represents the trajectory of a $S=1$ isentropic expansion.

Figure 2

Relationship between the transition temperature expected as a function of the entropy generated in the reaction [20].

Figure 3

Time evolution of the average speed of sound squared, ${\upsilon }_s^2$ in units of $c^2$, temperature (in MeV), density $\left({\text{fm}}^{-3}\right)$, and entropy per particle of a central collision of $\text{Au}+\text{Au}$ at $8000\text{MeV}$.

Figure 4

Time evolution of the information entropy obtained from central collisions of $\text{Ni}+\text{Ni}$ at 900 (top), 1050 (middle), and $1750\text{MeV}$ (bottom). Also listed are the asymptotic source size $\left(A\right)$ and the average entropy (see text).

Figure 5

Relationship between the entropy produced in the $\text{Ni}+\text{Ni}$ collisions at the energies listed in Fig. 4 and the asymptotic source sizes. Also shown are the values of the entropy generated by the reactions studied in Ref. 7.