Kaon production in heavy-ion collisions and kaon condensation in neutron stars

Abstract

The recent past witnesses the growing interdependence between the physics of hadrons, the physics of relativistic heavy-ion collisions, and the physics of compact objects in astrophysics. A notable example is the kaon which plays special roles in all the three fields. In this talk, we first review the various theoretical investigations of kaon properties in nuclear medium. We then present a detailed transport model study of kaon production and flow in heavy-ion collisions at SIS energies. Finally, We discuss the effects of the kaon in-medium properties extracted from heavy-ion data on neutron star properties, especially on the lowering of maximum mass of neutron stars with the onset of kaon condensation around 3ρ 0 .

Meson–nucleus potentials and the search for meson–nucleus bound states

“…The antikaon potential depth extracted in this way corresponds to an average K − momentum of about 0.5 GeV/c, where the main strength of the measured differential distributions is concentrated [167]. Within the uncertainties quoted, this value obtained for the antikaon potential depth is consistent with those extracted in [34,102,103,124,135] from the KaoS [106,107,175] and FRS data [176], from the FOPI A-A collision data [128,178] as well as from the pA KaoS data [46] (see above). It also agrees with a potential of the order of -100 MeV at saturation density (but for zero K − momentum), predicted in [97,23] and shown in Fig.…”

“…26) in the framework of the CBUU transport model [34,135] suggests a momentum-independent downward in-medium mass shift (or an attractive effective scalar K − potential V K − (ρ 0 )) of about -(100-120) MeV at density ρ 0 , assuming a linear dependence of the mass shift on the nuclear density. A similar K − potential of V K − (ρ 0 ) ≈ −110 MeV for kaons at rest has been extracted by Li et al [102,103,124] from a comparison of the KaoS data [106,107] with Figure 28: The measured K − /K + ratio as a function of the kinetic energy in the center-of-mass system for Al+Al collsions at 1.9 A GeV [178]: (a) not-corrected and (b) corrected for the 17% contribution of K − mesons from φ decays. Error bars represent the statistical uncertainties.…”

“…a promising probe of the kaon potential in dense matter, since it should push the K + mesons away from the nucleons and attract K − mesons towards the nucleons. The analysis of KaoS [106,107,[116][117][118][119], FOPI [120][121][122] and ANKE [123] on K + production in heavy-ion and proton-nucleus reactions established in the framework of transport approaches [34,103,124,125,126] and [28,44,111] that the K + meson indeed feels a moderately repulsive nuclear potential of about 20-30 MeV at normal nuclear matter density ρ 0 , in agreement with the above theoretical estimates. As an example of such analysis, Fig.…”

“…K − mass reduction [34,98,102,103,124,135]. An analysis of inclusive K − momentum spectra taken at KaoS [106,107,175] and FRS [176] (see Fig.…”