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

The production and propagation of antikaons—described by dynamical spectral functions <f>Ah(X,P→,M2)</f> as evaluated from a coupled channel <f>G</f>-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 <f>K−</f> spectra for 12C<f>+</f>12C and 58Ni<f>+</f>58Ni at 1.8 <f>A</f> GeV remain underestimated in the <f>G</f>-matrix approach as in the on-shell quasi-particle approximation whereas the preliminary spectra for <f>Au+Au</f> at <f>1.5 A</f> GeV are well described in both limits. This also holds approximately for the <f>K−</f> rapidity distributions in semi-central collisions of <f>Ni+Ni</f> at <f>1.93 A</f> 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 <f>K−</f> spectra to the low momentum regime. [Copyright &y& Elsevier]