In-medium effects in strangeness production in heavy-ion collisions at (sub)threshold energies

Abstract

We study the in-medium effects in strangeness production in heavy-ion collisions at (sub)threshold energies of (1-2)A GeV based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach. The in-medium modifications of the antikaon (K̄=K-,K̄0) properties are described via the self-consistent coupled-channel unitarized scheme based on a SU(3) chiral Lagrangian which incorporates explicitly the s and p waves of the kaon-nucleon interaction. This scheme provides the antikaon potential, spectral functions, and reaction cross sections as well as their dependence on baryon density, temperature, and antikaon momentum in the nuclear medium, which are incorporated in the off-shell dynamics of the PHSD. The in-medium modification of kaons (K=K+,K0) are accounted via the kaon-nuclear potential, which is assumed to be proportional to the local baryon density. The manifestation of the medium effects in observables is investigated for the K and K̄ rapidity distributions, pT spectra, the polar and azimuthal angular distributions, and directed (v1) and elliptic (v2) flows in C+C, Ni+Ni, and Au+Au collisions. We find - by comparison to experimental data from the KaoS, FOPI, and HADES Collaborations - that the modifications of (anti)kaon properties in nuclear matter are necessary to explain the data in a consistent manner. Moreover, we demonstrate the sensitivity of kaon observables to the equation of state of nuclear matter. ; Furthermore, we acknowledge support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) Grant No. BR 4000/7-1, by the Russian Science Foundation Grant 19-42-04101, and by the GSI-IN2P3 agreement under Contract No. 13-70. L.T. acknowledges support from the Deutsche Forschungsgemeinschaft (DFG, German research Foundation) under the Projects No. 383452331 (Heisenberg Programme) and No. 411563442 (Hot Heavy Mesons). Her research has been also supported by the Spanish Ministerio de Economía y Competitividad under Contract No. FPA2016-81114-P and Ministerio de Ciencia e Innovación under Contract No. PID2019-110165GB-I00. This project has, furthermore, received funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 824093 (STRONG-2020). Also we acknowledge support via the COST Action THOR, CA15213, and CRC-TR 211 "Strong-interaction matter under extreme conditions," Project No. 315477589-TRR 211. The computational resources were provided by the LOEWE Center for Scientific Computing and the "Green Cube" at GSI, Darmstadt.