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.
This work investigates the collective motion of kaons in heavy ion reactions at SIS energies (about 1-2 GeV/nucleon). A radial collective flow of $K^+$ mesons is predicted to exist in central Au + Au collisions, which manifests in a characteristic "shoulder-arm" shape of the transverse mass spectrum of the midrapidity $K^+$ mesons. The $K^+$ radial flow arises from the repulsive $K^+$ mean field in nuclear matter. In spite of a strong reabsorption and rescattering the attractive $K^-$ mean field leads as well to a collective radial flow of $K^-$ mesons. The $K^-$ radial flow, however, is different from that of $K^+$ mesons and can be observed by a characteristic "concave" structure of the transverse mass spectrum of the $K^-$ mesons emitted at midrapidity. The kaon radial flows can therefore serve as a novel tool for the investigation of kaon properties in dense nuclear matter.Comment: 30 pages RevTex, 5 PS figures, accepted for publication in Phys. Rev.
The importance of an isospin dependent nuclear mean field ͑IDMF͒ in regard to the pion production mechanism is studied for the reaction AuϩAu at 1 GeV/nucleon using the quantum molecular dynamics ͑QMD͒ model. In particular, the effect of the IDMF on pion spectra and the charged pion ratio are analyzed. It is found that the inclusion of a IDMF considerably suppresses the low-p t pions, thus leading to a better agreement with the data on pion spectra. Moreover, the rapidity distribution of the charged pion ratio appears to be sensitive to the isospin dependence of the nuclear mean field.
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