Nucleon-$Δ$ elastic cross section in isospin-asymmetric nuclear medium with inclusion of scalar-isovector $δ$ meson field

Abstract

The production, dynamic evolution, and decay of $Δ$ particles play a crucial role in understanding the properties of high baryon density nuclear matter in intermediate-energy heavy-ion collisions. In this work, the energy-, density-, and isospin-dependent nucleon-$Δ$ elastic cross section ($σ^{*}_{N Δ}$) is studied within the relativistic Boltzmann-Uehling-Uhlenbeck framework, in which the $δ$ meson field is further considered. The results show that the $δ$ and $ρ$ meson related exchange terms have a nonnegligible contribution to the $σ^{*}_{N Δ}$ compared to only considering the $ρ$ meson exchange terms, although there is a significant cancellation on the cross section among these meson exchange terms. In addition, due to the different effects of the medium correction on the effective mass of neutrons, protons, and differently charged $Δ$s, the individual $σ^{*}_{N Δ}$ exhibits an ordered isospin-asymmetry ($α$) dependence, and $σ^{*}_{nΔ}$ and $σ^{*}_{pΔ}$ have opposite $α$ dependencies. And the $α$ dependence of the ratio $R(α)=σ^{*}(α)/σ^{*}(α=0)$ for $nΔ$ reaction channels follow $nΔ^{++}>nΔ^{+}>nΔ^{0}>nΔ^{-}$, while for $pΔ$ it is $pΔ^{-}>pΔ^{0}>pΔ^{+}>pΔ^{++}$. Moreover, the results also indicate that the isospin effect on the $σ^{*}_{N Δ}$, which is dominantly caused by the isovector $ρ$ and $δ$ meson fields, is still pronounced at densities up to 3 times normal nuclear density. Finally, a parametrization of the energy-, density-, and isospin-dependent $NΔ$ elastic cross section is proposed based on the microscopic calculated results, and the in-medium $σ^{*}_{N Δ}$ in the energy range of $\sqrt{s}$=2.3$\sim$3.0 GeV can be well described.