Speaker
Description
The possible existence of deeply-bound $\bar K$-nuclear bound states (kaonic nuclei) has been widely discussed as a consequence of the strongly attractive $\bar K N$ interaction in I = 0 channels. The investigation of kaonic nuclei can provide unique information about the $\bar K N$ interaction below the threshold, which is still not fully understood. For the simplest kaonic nucleus, $\bar KNN$, we performed an experimental search using the in-flight $^3$He$( K^-, n)$ reactions at 1 GeV/$c$ (J-PARC E15). With the $\Lambda pn$ final state reconstructed, we observed a significant peak below the $K^-pp$ mass-threshold in the $\Lambda p$ invariant-mass spectrum, which can be interpreted as the ``$K^-pp$’’ bound state. To further understand the kaonic nuclei, we have proposed and prepared the E80 experiment to precisely measure the $\bar K NNN$ system as a first step toward the comprehensive study of the light kaonic nuclei from the “$\bar K N$” (=$\Lambda$(1405)) to“$\bar K NNNN$.” Through the experiments and detailed theoretical calculations, we will unravel the nature of the kaonic nuclei from the property changes depending on the mass number $A$. We will discuss the $\bar KNN$ bound state observed at J-PARC E15 and the future prospects of light kaonic nucleus studies at J-PARC starting with the E80 experiment.
