Effect of Delta potential on the pion-/pion+ ratio in heavy-ion collisions at intermediate energies

Abstract

Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck(IBUU) transport model, effects of $\Delta$ resonance potential on the free n/p and ${\pi }^{-}/{\pi }^{+}$ ratios in the central collision of ${}^{197}Au{+}^{197}Au$ at beam energies of 200 and 400 MeV/A are studied. It is found that the effect of $\Delta$ potential on the ratio of pre-equilibrium free $n/p$ is invisible. The effect of $\Delta$ isovector potential on the kinetic energy integrating ratio of ${\pi }^{-}/{\pi }^{+}$ may be observable only at lower incident beam energies and with stiffer symmetry energy. The strength of the $\Delta$ isoscalar potential affects the height of the ${\pi }^{-}/{\pi }^{+}$ ratio around the Coulomb peak but does not affect the kinetic energy integrating ratio of ${\pi }^{-}/{\pi }^{+}$. In heavy-ion collisions at intermediate energies, relating to the question of non-conservation of energy on $\Delta$ or $\pi$ productions, one can replace the $\Delta$ potential by nucleon isoscalar potential especially a soft symmetry energy is employed.

Comments: 5 pages, 9 figures, revised version, accepted by PRC