An excitation function of K− and K+ production in Au+Au reactions at the AGS

Abstract Mid-rapidity spectra and yields of K − and K + have been measured for Au+Au collisions at 4, 6, 8, and 10.7 AGeV. The K − yield increases faster with beam energy than for K + and hence the K − /K + ratio increases with beam energy. This ratio is studied as a function of both s and s − s th which allows the direct comparison of the kaon yields with respect to the production threshold in p+p reactions. For equal s − s th the measured ratio K − /K + =0.2 at energies above threshold in contrast to the K − /K + ratio of near unity observed at energies below threshold. The use of the K − /K + ratio to test the predicted changes of kaon properties in dense nuclear matter is discussed.