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

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 b eam energy than for K+ and hence the K-/K+ ratio increases with beam energy . This ratio is studied as a function of both root s and root s - root s(th ) which allows the direct comparison of the kaon yields with respect to the production threshold in p + p reactions. For equal root s - root 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. (C) 2000 Elsevier Science B.V. All rights rese rved.