Speaker
Description
The strongly attractive antikaon–nucleon ($\bar K N$) interaction in the $I=0$ channel has led to the widespread interpretation of the $\Lambda(1405)$ resonance as a $\bar K N$ bound state, motivating the study of exotic antikaon-nuclear bound systems known as kaonic nuclei. At J-PARC, we have carried out a systematic experimental program to search for and study these systems, extending from the elementary $\bar K N$ interaction to few-body nuclei.
In the J-PARC E15 experiment, we searched for the simplest kaonic nucleus, $\bar K NN$, via the $^3\mathrm{He}(K^-, n)$ reaction, detecting the $\Lambda$ and proton from its decay and identifying the neutron through missing-mass analysis. The observation of a distinct peak below the $K^-pp$ mass threshold provided strong evidence for its formation. To better understand the fundamental interaction governing such states, we also conducted the E31 experiment, yielding a key input by precisely determining the $\Lambda(1405)$ line shape through the $d(K^-,n)\pi\Sigma$ reaction.
Building on these successes, we are currently upgrading our spectrometer for the newly approved E80 experiment, which will extend our investigation to the $\bar K NNN$ system and heavier $\bar K$–nuclear systems. This systematic approach, exploring the mass-number dependence of kaonic nuclei, is expected to provide definitive insights into the nature of kaonic nuclei. We summarize the key results from E15 and E31, and outline future prospects of this systematic study, beginning with E80.