Probing nuclear bubble configuration by the $\pi^{-} / \pi^{+}$ ratio in heavy-ion collisions

Abstract

It is theoretically and experimentally argued that there may exist bubble or toroid-shaped configurations in some nucleus systems. Based on the isospin-dependent transport model of nucleus-nucleus collisions, here we propose a method to probe the bubble configuration in nucleus. That is, one could use the value of π − /π + ratio especially its kinetic energy distribution in head-on collision at intermediate energies to probe whether there is bubble configuration or not in projectile and target nuclei. Due to different maximum compressions and the effect of symmetry energy, the value of π − /π + ratio in the collision of bubble nuclei is evidently larger than that in the collision of normal nuclei.

Determination of the density region of the symmetry energy probed by the ${\pi }^{-}/{\pi }^{+}$ ratio

“…In this study, pion production in our used transport model is the same as that shown in [50] but without medium corrections of both elastic and inelastic baryon-baryon scattering cross sections. We use the Skyrme-type parametrization for the isoscalar mean field [51][52][53], i.e.…”

Initialization effects of nucleon profile on the π yields in heavy-ion collisions at medium energies

“…Recently, Stone et al have systematically studied the effects of the proton and neutron density distributions in central HIC, and found that the maximal neutron-to-proton ratio during the collision process is quite sensitive to the initial-state density distributions [19], where the different maximum neutron-to-proton ratios would result in a difference of π productions. Therefore, it was also shown recently that π mesons provide a remarkably good probe to study bubble structure inside nuclei [20]. On the surface of the nucleus, the density distributions of protons and neutrons of some nuclides were also obtained using x-ray and nuclear spectral analysis of antiprotons, respectively [21].…”