Subthreshold pion production within a transport description of central Au+Au collisions

TL;DR

This paper uses a transport model to study pion production in central Au+Au collisions, revealing sensitivities to the nuclear mean field and symmetry energy, and proposing new experimental observables for high-density nuclear matter.

Contribution

It introduces the use of the pBUU transport model to analyze pion production and suggests novel high-energy pion ratio measurements to probe the symmetry energy at high densities.

Findings

Net pion yield tests momentum dependence of nuclear mean field

Pion ratios at high energies can distinguish symmetry energy variants

Results differ from predictions of other transport models

Abstract

Mapping out the equation of state (EOS) of nuclear matter is a long standing problem in nuclear physics. Recent emphasis is onto the density dependence of the symmetry energy, with experiments needing dedicated symmetry-energy observables. Towards the latter goal, we employ pBUU transport model to simulate pion production in heavy ion collision (HIC). We find that the net pion yield tests the momentum dependence of nuclear mean field (MF). In exploring the sensitivity of pion observables to the symmetry energy at higher than normal densities, we find that our calculations of pion ratios contradict, at some level, predictions from both IBUU and ImIQMD models. We propose to employ the pion ratio in the high-energy tail of spectra in future experiments, to distinguish between different variants of high-density symmetry energy.