Light Kaonic Nuclei at J-PARC

The potential existence of deeply bound $\bar K$-nuclear systems, known as kaonic nuclei, has been extensively discussed due to the strong attraction in the $\bar K N$ interaction, particularly in the isospin $I = 0$ channel. In the lightest such system, the $\bar KNN$ configuration, we observed a prominent peak structure interpreted as the ``$K^-pp$’’ bound state in the $^3$He$(K^-,n)$ reaction at J-PARC. To deepen our understanding of kaonic nuclei, we have planned and prepared an experiment targeting the $\bar K NNN$ system via the $^4$He$(K^-,N)$ reaction. This effort marks the first step toward a systematic investigation of light kaonic nuclear systems, ranging from the $\bar K N$ state (identified with the $\Lambda(1405)$) to more complex configurations such as $\bar K NNNN$ and beyond. By combining these experimental studies with detailed theoretical calculations, we aim to uncover the nature of kaonic nuclei by examining how their properties evolve with increasing mass number $A$.