Speaker
Description
A previous study of symmetry energy using pion production in heavy-ion collisions close to threshold is revisited [1,2]. Formerly neglected contributions, amounting to non-resonant pion production [3], have now been included in the dcQMD transport model. Their impact on total charged pion multiplicity and charged pion ratio is investigated in detail. Following the finding of relatively strong in-medium modification of transition matrix elements for elastic nucleon-nucleon scattering reported in Ref. [4], transition matrix elements for inelastic collisions are adjusted using simple scaling factors depending on density and isospin asymmetry. Their strengths and other quantities of interest, such as Δ(1232) in-medium potentials, neutron-proton effective mass difference and density dependence of symmetry energy, are determined from comparison to experimental data for integrated charged pion multiplicity and ratio [5,6]. It is found that no in-medium modifications of NN→NΔ transition matrix elements are required, while the strength of the isoscalar Δ(1232) potential at saturation is less attractive than that of the nucleon. Values for neutron-proton effective mass difference and slope of the symmetry energy at saturation compatible with world averages are deduced [7].
- M.D. Cozma, Eur. Phys. J. A 57, 309 (2021);
- J. Estee et al., Phys. Rev. Lett. 126, 162701 (2021);
- O. Buss et al., Eur. Phys. J. A 29, 189 (2006);
- M.D. Cozma, Phys. Rev. C 110, 064911 (2024);
- W. Reisdorf et al., Nucl. Phys. A 848, 366 (2010);
- G. Jhang et al., Phys. Lett. B 813, 136016 (2021);
- M.D. Cozma, in preparation.
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