Antikaon production in A+ A collisions at SIS energies within an off-shell G-matrix approach

Abstract

The production and propagation of antikaons—described by dynamical spectral functions A h(X, P → ,M 2) as evaluated from a coupled channel G-matrix approach—is studied for nucleus–nucleus collisions at SIS energies in comparison to the conventional quasi-particle limit and the available experimental data using off-shell transport theory. We find that the K − spectra for 12C+ 12C and 58Ni+ 58Ni at 1.8 A GeV remain underestimated in the G-matrix approach as in the on-shell quasi-particle approximation whereas the preliminary spectra for Au+Au at 1.5 A GeV are well described in both limits. This also holds approximately for the K − rapidity distributions in semi-central collisions of Ni+Ni at 1.93 A GeV. However, in all limits considered there is no convincing description of all spectra simultaneously. Our off-shell transport calculations, furthermore, demonstrate that the strongest in-medium effects should be found for low antikaon momenta in the center-of-mass frame, since the deceleration of the antikaons in the attractive Coulomb and nuclear potentials and the propagation to the on-shell mass induces a net shift and squeezing of the K − spectra to the low momentum regime.