J-PARC E15 and E80 Experiments
-- A search for deeply-bound kaonic nuclear states by the in-flight (K-,N) reaction --
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.
The J-PARC E15 experiment investigated the lightest such system, the $\bar{K}NN$ configuration, and observed a prominent peak structure interpreted as the "$K^-pp$" bound state in the $^3$He$(K^-,n)$ reaction, providing strong evidence for the existence of kaonic nuclei.
Building upon this success, the planned J-PARC E80 experiment is set to deepen our understanding. The initial focus will be on 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 $A$.