Study of low energy ^^-KN interaction

我们一直在研究核子与K介子（K介子）之间的强相互作用，即用K介子代替氢原子中的一个电子。当K介子停留在气态氢靶中时，产生K介子氢原子。从连续退激发射的X射线的能量给出能量移位和线宽加宽从电磁值，特别是对于过渡到地面。因此，对这种X射线的精确测量给出了低能极限下^^-KN相互作用的最基本信息。我们在KEK PS-E228（KpX）上成功地观测到了K介子氢2 p到1 s跃迁，并开始了DAΦNE-DEAR实验，通过K-d和K-p原子X射线观测详细研究了相互作用的同位旋依赖性，但研究的道路并不一定是一帆风顺的。最大的问题是，加速器的操作已经大大推迟了时间表，超出了预期。而且，我们还受到了巨大的背景影响，超出预期100倍。另一方面，这一困难促进了与Akaishi等人的理论的联合研究。根据我们的GSI实验S218揭示的π介子可以存在于核内的结果，以及我们的KpX结果表明K介子和质子之间具有强吸引力的性质，K介子可以在核内形成稳定的状态。如果原子核内部存在深度束缚的K介子态，则可以更直接、更有效地实现本研究计划的目的。到目前为止，我们已经能够在KEK（PS-E471）开始寻找深层束缚的K介子态。

We have been studying the strong interaction between nucleon and K meson (kaon) by replacing an electron in the hydrogen atom with kaon, which has a strange quark. When, kaon stops in the gaseous hydrogen target, kaonic hydrogen atom is generated. The energy of the emitted x ray from the successive deexcitation gives energy shift and line width broadening from the electromagnetic value, especially for the transition to the ground. Therefore, the precise measurement of this X rays gives the most basic information of the ^^-KN interaction at the low energy limit. We have succeeded to observe the kaonic hydrogen 2p to 1s transition at KEK PS-E228 (KpX), and began the DAΦNE-DEAR experiment to deduce the isospin dependence of the interaction by detailed study both on K-d and K-p atom X rays observations.However, the way of the research is not necessarily smooth. The biggest problem is that the accelerator operation had been delayed substantially from the schedule away beyond the expectation. Moreover, we had been suffered by the huge background, which exceeded the expectation by 100 times more. On the other hand, this difficulty promoted a joint research with the theory with Akaishi et al. It is shown that the kaon may form a stable state inside the nuclei, based on the results i) our GSI experiment S218 revealed that the pi meson can exist inside the nuclei, and ii) our KpX result indicated strongly attractive nature between kaon and proton. If there exist deeply bound kaonic state inside nuclei, the purpose of this research program can be achieved more directly in more efficient way. By the present grant, we were able to start the search for the deeply-bound kaonic state at KEK (PS-E471).