Kaon and pion emission in asymmetric C+Au and Au+C collisions at 1.0A GeV and 1.8A GeV

The emission of K+ and ± mesons has been studied in the asymmetric collision system Au+C and in the inverse reaction C+Au at 1.0A GeV (and at 1.8A GeV for C+Au only) in order to extract the effective source rapidities based on their distribution in the pt-y plane. The extracted source rapidity of K+ mesons is about ys/ybeam=0.25 at both incident energies [y(Au)=0,y(C)=ybeam]. This corresponds to a reaction volume consisting of the C nucleus and a tube cut out of the Au nucleus. In clear contrast, the source rapidities of ± mesons vary from ys/ybeam=0.5 in peripheral collisions (corresponding to NN interactions) to about ys/ybeam<0.33 in central reactions. The multiplicities of K+ and are compared to symmetric collision systems and, together with detailed transport model calculations, are used to study the sensitivity to the nuclear equation of state.