标题： 重离子反应中的K介子挤压效应 显示英文标题

标题： Kaon squeeze-out in heavy ion reactions

摘要： 研究了能量为 1-2 A.GeV 的重离子反应中，近零快度发射的$K^+$和$K^-$介子表现出的$K^+$和$K^-$介子挤压效应，即横向不对称性。结果表明，这些介子的介质势对挤压效应信号有很强的影响。排斥性的$K^+$- 核介质势导致近零快度处明显的非平面发射的$K^+$。 使用$K^+$势能，我们很好地再现了$K^+$方位角分布的实验数据。 发现吸引性的$K^-$-核势能在很大程度上抵消了$K^-$介子在入射粒子和靶残余物上的再散射和再吸收的影响（即阴影效应）。 这导致中快度$K^-$介子在横动量高达 0.8 GeV/c 的方位角各向同性发射。 由于众所周知，单独的阴影效应会导致粒子发射明显的面外偏好，特别是在高横动量下，$K^-$介子的面外偏好的消失可以作为吸引性$K^-$势能的一个明确信号。 我们还应用了协变形式的 kaon 动力学来研究挤压效应。 讨论了理论与实验之间的差异以及可能的解决方案。 显示英文摘要

摘要： 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.