The isoscalar and isovector in-medium potentials of the Δ(1232) baryon are studied by comparing QMD transport model predictions for pion production in heavy-ion collisions below 0.8 GeV/nucleon impact energy to available experimental data [1,2]. The best description is achieved for an isoscalar potential moderately more attractive than the nucleon optical potential and a rather small isoscalar relative effective mass m*Δ ≈ 0.45. For the isovector component only a constraint between the potential's strength at saturation and the isovector effective mass difference can be extracted, which depends on quantities such as the slope of the symmetry energy and the neutron-proton effective mass difference [3]. These results are incompatible with the usual assumption, in transport models, that the Δ(1232) and nucleon potentials are equal. The density dependence of symmetry energy can be studied using the high transverse momentum tail of pion multiplicity ratio spectra. Results are however correlated with the value of neutron-proton effective mass difference [4]. This region of spectra is shown to be affected by uncertain model ingredients such as the pion potential or in-medium correction to inelastic scattering cross-sections at levels smaller than 10%. A feasibility study of the symmetry energy using the recently published HADES experimental data for pion production in AuAu collisions at s^1/2 ≈ 2.4 GeV [5] will also be briefly discussed.

1. W. Reisdorf et al. (FOPI Collaboration), Nucl. Phys. A 848, 366 (2010).
2. G. Jhang et al. (SΠRIT Collaboration), Phys. Lett. B 813, 136016(2020).
3. M.D. Cozma, M.B. Tsang, Eur. Phys. J. A 57, 309 (2021).
4. J. Estee et al. , Phys. Rev. Lett. 126, 162701 (2021).
5. J. Adamczewski-Musch et al. (HADES Collaboration), Eur. Phys. J. A 56, 259 (2020).