In-medium pion dispersion relation and medium correction of $Nπ\leftrightarrow Δ$ near the threshold energy of pion production

Abstract

Transport models cannot simultaneously explain very recent data on pion multiplicities and pion charged ratios of Sn+Sn in the reaction at 0.27 A GeV. This stimulates further investigations on the pion dispersion relation, in-medium $Nπ\to Δ$ cross sections and $Δ\to N π$ decay widths near the threshold energy or at subthreshold energy of pion production in isospin asymmetric nuclear matter. In this study, the pion dispersion relation, in-medium $Nπ\to Δ$ cross section and $Δ\to N π$ decay width near the threshold energy are investigated in isospin asymmetric nuclear matter by using the one-boson-exchange model. With the consideration of the energy conservation effect, the in-medium $Nπ\toΔ$ cross sections are enhanced at $s^{1/2}<1.11$ GeV in nuclear medium. The prediction of pion multiplicity and $π^-/π^+$ ratios near the threshold energy can be modified if this effect is considered in transport model simulations.