Effects of pion potential and nuclear symmetry energy on theπ−/π+ratio in heavy-ion collisions at beam energies around the pion production threshold

Abstract

Within the framework of the isospin-dependent Boltzmann-Uehling-Uhlenbeck(IBUU) transport model, we studied the effects of the pion potential and the symmetry energy on the pion production in the central 197 Au + 197 Au collisions around the pion production threshold. It is found that the pion potential has opposite effects on the value of π − /π + ratio at low and high pion energies. The effect of the pion potential on the total π − /π + ratio becomes larger in heavy-ion collisions at beam energies below the pion production threshold. And at beam energies below the pion production threshold, with the pion potential, the effect of the symmetry energy on the π − /π + ratio becomes smaller compared with that above the pion production threshold.

A possible probe of the new fifth force

“…There are still other mechanisms which cause the enhancement of energetic π − /π + ratio with the fifth force in heavy-ion collisions at intermediate energies. For example, based on the ∆-hole model and the relativistic Vlasov-Uehling-Uhlenbeck transport model with the relativistic nonlinear NLρ interaction, the pion p-wave potential may enhance the value of the energetic π − /π + ratio at pion kinetic energies above 200 MeV [38], although the pion potential may have no effects at pion kinetic energies around 200 MeV [41]. Nevertheless, the evident enhancement of energetic π − /π + ratio at pion kinetic energies around 900 MeV are mostly due to the fifth force because the very energetic pions almost have no much time to suffer the mean-field potential from surrounding nuclear matter.…”

Effects of symmetry energy in $^{132}\rm {Sn}+^{124}\rm {Sn}$ reaction at 300 MeV/nucleon

“…In this model, the isospin-, density-and momentumdependent pion potential is also included [22]. More details about this model can be found in Ref.…”

“…More details about this model can be found in Ref. [20][21][22]. Sensitivities of neutron to proton ratio and π − /π + ratio to nuclear symmetry energy have in fact been examined by Li in central 124 Sn+ 124 Sn reactions at 400 MeV/nucleon in 2003 with an Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model [24].…”

“…In order to check whether the above measurements can probe the symmetry energy around twice saturation * Electronic address: yonggaochan@impcas.ac.cn density, we in this work study the probed density region of the symmetry energy of some symmetry-energysensitive observables in 132 Sn + 124 Sn reaction at 300 MeV/nucleon. Our studies are based on the newly updated Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, which includes physical considerations of nucleon short-range correlations, in-medium inelastic baryon-baryon cross section and momentumdependent pion potential [20][21][22]. Our studies show that neutron to proton ratio and π − /π + ratio in central 132 Sn + 124 Sn reaction at 300 MeV/nucleon mainly probe the symmetry energy around saturation density, i.e., probe the symmetry energy in the density region 1-1.5 times saturation density.…”

The influence of $\pi$N potential on the collective flow of pion mesons in heavy-ion collisions at intermediate energies

“…文献 [12] 中采用了考 虑π介子与核子相互作用势(πN 势)的pBUU模型, 计 算结果却显示π − /π + 产额比非常不敏感于对称能. 文 献 [13] 中在IBUU 模型中也考虑了πN 势, 研究表明 当入射能量低于π 介子产生阈值时, π − /π + 产额比 会受到πN势影响. 文献 [14]中则指出, 核介质对π 介 子产生阈值的修正会影响π − /π + 产额比.…”