Transport simulations with π and Δ in-medium properties

Abstract

Transport simulations including in-medium properties derived in a microscopic π +N N −1 + ∆N −1 model in infinite nuclear matter are presented. In-medium pion dispersion relations, partial ∆ decay widths, pion absorption cross sections and ∆ cross sections are incorporated into the transport description by means of a local-density approximation. Strong modifications of π and ∆ production and absorption rates are found, but only small effects on pion observables.

Off-shell pions in Boltzmann-Uehling-Uhlenbeck transport theory

“…As an observable effect in heavy-ion collisions at 1 A GeV, we have demonstrated the low p t enhancement of the pion yield due to the off-shell pion propagation, which is in agreement with earlier BUU calculations [11,12,13] using the in-medium pion dispersion relation. We expect, that the pion off-shellness will also influence other observables, which are not covered in this work, e.g.…”

“…The soft pion enhancement due to the in-medium pion modifications has been observed in [11] in agreement with BUU studies in [12,13]. As has been pointed out in [11], the overall effect of the in-medium modifications on the pion observables is small due to the fact, that the observed pions are emitted from the surface region of the system, where the in-medium modifications are not important. However, by multistep processes, pions influence other particles, e.g.…”

“…The explicit in-medium modification of the ∆-width in BUU has been studied earlier in Refs. [11,25], where a quite weak effect on pion observables in heavy-ion collisions and on γ-absorption cross section on nuclei was found. Finally, it is straightforward to generalize the ∆-hole model including higher baryonic resonances which will then also contribute to the pion spectral function.…”

“…[10,21] by assuming that Im Π c ∝ ρ N and neglecting Re Π c in the propagation of the pions. Earlier BUU studies [11,12,13] within the on-shell approximation have shown that the inclusion of the real part of the pion optical potential results in an enhanced soft pion yield. However, our attempted treatment of the off-shell pion propagation within the formalism of Refs.…”

“…The transport simulations with in-medium pion and ∆ properties have been recently performed by Helgesson and Randrup in a series of works (see [11] and Refs. therein) employing the quasiparticle approximation for pions.…”