H. Menzel et al., First measurement of antikaon phase-space distributions in nucleus-nucleuscollisions at subthreshold beam energies, PHYS LETT B, 495(1-2), 2000, pp. 26-32
Differential production cross sections of K- and K+ mesons have been measur
ed as function of the polar emission angle in Ni+Ni collisions at a beam en
ergy of 1.93 A GeV. In near-central collisions, the spectral shapes and the
widths of the rapidity distributions of K- and K+ mesons are in agreement
with the assumption of isotropic emission. In non-central collisions, the K
- and K+ rapidity distributions are broader than expected for a single ther
mal source. In this case, the polar angle distributions are strongly forwar
d-backward peaked and the nonisotropic contribution to the total yield is a
bout one third both for K+ and K- mesons. The K- /K+ ratio is found to be a
bout 0.03 independent of the centrality of the reaction. This value is sign
ificantly larger than predicted by microscopic transport calculations if in
-medium modifications of K mesons are neglected. (C) 2000 Elsevier Science
B.V. All rights reserved.