The charged pion multiplicity ratio in intermediate energy heavy-ion collisions is one of the promising probes for the study of the density dependence of symmetry energy above the saturation point. It is however sensitive to poorly known quantities such as the isoscalar and isovector Delta(1232) potentials in nuclear matter [1]. For the existing experimental data sets uncertainties due to the latter are dominating. It is shown that, by including the ratio of average transverse momenta of charged pions in the list of fitted observables, the noted problem can be circumvented [2]. A realistic description of this observable requires accounting for the interaction of pions with the dense nuclear matter environment by the incorporation of the so called S and P-wave pion optical potentials. This is performed within the framework of a QMD transport model that enforces the conservation of the total energy of the system and incorporates information about these potentials gained by the experimental study of pionic atoms and pion-nucleus scattering and also from theoretical hadronic models and chiral perturbation theory. It is shown that constraints for the slope of the symmetry energy at saturation density and the strength of the Delta(1232) isovector potential can thus be simultaneously extracted [2]. Comparing to the forthcoming experimental data (SPIRIT Collaboration) for subthreshold pion production will require knowledge of the isoscalar component of the Delta(1232) potential as well. Using a suitable parametrization for it, information regarding its depth and momentum dependence is extracted from a comparison with experimental total pion multiplicities [3].

1. M.D. Cozma, Phys. Lett. B 753, 166 (2016).
2. M.D. Cozma, Phys. Rev. C 95, 014601 (2017).
3. M.D. Cozma, in preparation.