Speaker
Fuminori Sakuma
(RIKEN)
Description
The possible existence of strongly-bound $\bar K$ nuclear-states has been widely discussed as a consequence of the strongly attractive $\bar K N$ interaction in I = 0 channels. Experimentally, however, available information is not sufficient to discriminate between a variety of conflicting interpretations so far. In this situation, we have performed an experimental search for the simplest kaonic nuclear bound state, $\bar KNN$, by the in-flight $K^-$ $+$ $^3$He reactions at 1 GeV/$c$ (J-PARC E15). The experiment investigates the $\bar KNN$ state both in the formation via $^3$He$(K^-, n)X$ missing-mass spectroscopy and its decay via invariant-mass spectroscopy using $^3$He$(K^-, \Lambda p)n$ channel, respectively. The first physics data-taking was performed at the K1.8BR beam-line in 2013. With this data-set, we have observed a significant bump structure around the $K^-pp$ mass-threshold in the $\Lambda p$ invariant-mass spectrum in the exclusive $^3$He$(K^-, \Lambda p)n$ analysis [PTEP(2016)051D01]. We will discuss the possible existence of the $\bar KNN$ states by combining the production- and the decay-channel analyses. In addition, we will present the latest results of the second data-taking performed in 2015, where much improved data statistics of the $^3$He$(K^-, \Lambda p)n$ channel was accumulated.
