Effect of hyperons on phase coexistence in strange matter

The study of the liquid gas phase transition in the fragmentation of nuclei in heavy ion collisions has been extended to the strangeness sector using the statistical model for multifragmentation. Helmholtz's free energy, specific heat, and a few other thermodynamic observables have been analyzed in order to examine the occurrence of phase transition in the strange matter. The bimodal behavior of the largest cluster formed in fragmentation also strongly indicates a coexistence of both the phases. The presence of hyperons strengthens the signals and also shifts the transition temperature to lower values.

Figure 1

Variation of Helmholtz's free energy per nucleon (upper panel), entropy per nucleon (middle panel), and specific heat per nucleon (bottom panel) with temperature for two fragmenting systems having the same $A_0=128$, $Z_0=50$ but different $H_0=8$ (black solid lines) and $H_0=0$ (red dashed lines).

Figure 2

Largest cluster probability distribution for four different fragmenting systems having same $A_0=128$, $Z_0=50$ but different $H_0=8$ (black solid line), $H_0=4$ (blue dotted line), $H_0=2$ (green dash dotted line), and $H_0=0$ (red dashed line). Calculations are done at constant temperature $T=6.065$ MeV.

Figure 3

Variation of transition temperature ($T_p$) with the total strangeness content of the fragmenting system.

Figure 4

Variation of average charge of the largest cluster ($Z_{\max }$) with temperature ($T$) for two fragmenting systems having the same $A_0=128$, $Z_0=50$ but different $H_0=8$ (black solid line) and $H_0=0$ (red dashed line).

Figure 5

Variation of temperature ($T$) with excitation energy ($E^{*}$) for two fragmenting systems having the same $A_0=128$, $Z_0=50$ but different $H_0=8$ (black solid line) and $H_0=0$ (red dashed line).

Figure 6

Variation of pressure with volume for two fragmenting systems having the same $A_0=128$, $Z_0=50$ but different $H_0=8$ (solid lines) and $H_0=0$ (dashed lines) at four different temperatures $T=5.0$, 5.5, 6.0, and 6.5 MeV.

Figure 7

Variation of average charge of the largest cluster ($Z_{max}$) (upper panel) and specific heat per nucleon (lower panel) with temperature ($T$) by switching on (blue dashed lines) and switching off (black solid lines) the Coulomb interaction. All the calculations are done for the fragmentation of a hypernucleus having $A_0=128$ baryons, $Z_0=50$ protons, and $H_0=8$ hyperons.