Kaon squeeze-out in heavy ion reactions
Z.S. Wang - C. Fuchs - A. Faessler - T. Gross-Boelting
Institut für Theoretische Physik der Universität Tübingen, D-72076 Tübingen, Germany
Received: 15 September 1998 / Revised version: 18 January 1999 Communicated by P. Schuck
Abstract
The squeeze-out phenomenon of K+ and K- mesons, i.e. the azimuthal asymmetry of
K+ and K- mesons emitted at midrapidity in heavy ion reactions, is investigated for beam
energies of 1-2 A.GeV. It is found that the squeeze-out signal is strongly affected by
in-medium potentials of these mesons. The repulsive K+-nucleus potential gives rise to a
pronounced out-of-plane emission of K+'s at midrapidity. With the K+ potential we
reproduce well the experimental data of the K+ azimuthal distribution. It is found that the
attractive K--nucleus potential cancels to a large extent the influence of rescattering
and reabsorption of the K- mesons on the projectile and target residuals (i.e. shadowing).
This results in an azimuthally isotropic emission of the midrapidity K- mesons with
transverse momentum up to 0.8 GeV/c. Since it is well accepted that the shadowing alone would
lead to a significant out-of-plane preference of particle emission, in particular
at high transverse momenta, the disappearance of the out-of-plane preference for the K-
mesons can serve as an unambiguous signal of the attractive K- potential. We also apply a
covariant formalism of the kaon dynamics to the squeeze-out phenomenon. Discrepancies between
the theory and the experiments and possible solutions are discussed.
Copyright Springer-Verlag
