Search for deeply bound kaonic state

为了观察深度束缚的K介子核态，我们在KEK-PS进行了一系列实验（E471/E549/E570）。当K介子与核的相互作用是强吸引时，K介子吸引邻近的核子，形成高密度的核物质，形成深度束缚的K介子核，当束缚变大时，K介子核的主要衰变通道关闭，K介子核的宽度变窄。为此，我们测量了^4He（K-停止，N）反应的中子/质子谱。在中子/质子谱中，我们没有观察到窄峰。从中子谱和质子谱得到了窄K介子态形成速率的严格上限。我们曾经报道过E471实验中质子谱中出现的一个窄峰--S_0（3115）--，这是由于E549实验中的实验伪影造成的。由于E549/E570实验数据的高统计性，我们成功地测量了超子（Λ或Λ）和核子（s）（n/p或d）的能量和角关联。特别是对Λnd通道的独家测量，为研究具有较宽宽度的K介子核态打开了大门。我们现在计划在J-PARC进行具有^3He（飞行中K-，n）反应的K-pp系统的独家测量。

In order to observe deeply bound kaonic nuclear states, we carried out series of experiments (E471/E549/E570) at KEK-PS. If the interaction between kaon and nucleus is strongly attractive, K meson attracts neighboring nucleons and can form high density nuclear matter and can form deeply bound kaonic nuclei.When the binding becomes large, its major decay channel closes and the kaonic nuclei can have narrow widths. To this end, we measured neutron/proton spectra from ^4He(K-stopped, N) reactions. In both of neutron/proton spectra, we do not observe narrow peaks in the inclusive spectra. Tight upper limits for the formation rate of narrow kaonic states were obtained ftom both of neutron and proton spectra. We once reported a narrow peak -S0(3115)- in the proton spectrum in E471 experiment, it was found to be due to the experimental artifacts from the in results of the dedicated high-statistics experiment, E549.Thanks to the high statistics of E549/E570 data, we could successfully measure the energy and angular correlation of hyperon (Λ or Σ) and nucleon(s) (n/p or d). Especially, exclusive measurement of Λnd channel opened the door to investigate the gate to study the kaonic nuclear states with relatively broad widths. We are now planning to do exclusive measurement of K-pp system with ^3He(in-flight K-,n) reaction at J-PARC.