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.Comment: 24 pages Latex using Elsevier style, 7 PS figures, accepted for
publication in Euro. Phys. Jour.
