J-PARC E15

Over the last decade, kaonic nuclear states have been studied extensively. In particular, the simplest state, $K^-pp$, is widely discussed in terms of its binding energy and width, since such simplest state is quite sensitive to the $\bar{K}N$ interaction. There are various theoretical predictions of the $K^-pp$ state at present, thus it is quite important to compare the theoretical calculations with experimental studies. However, the experimental situation is also controversial; the DISTO and FINUDA collaborations have claimed observations of the deeply-bound $K^-pp$ state, while the HADES and LEPS groups recently reported null results of the $K^-pp$ searches. Therefore, we need to investigate the $K^-pp$ state in different reactions and to understand background process, such as multi-nucleon absorption processes of $K^-$. In the J-PARC E15 experiment, the $K^-pp$ search is performed via the $^3\mathrm{He}(K^- ,n)$ reaction at 1.0 GeV/c. A forward-going neutron is detected by a neutron counter with 15 m flight length, and decay particles from $K^-pp$ are simultaneously measured by a cylindrical detector system that surrounds a liquid $\rm{{}^3He}$ target system. In March and May, 2013, we carried out the first physics data-taking with 5x$10^9$ incident kaons on the $\rm{{}^3He}$ target, and we have obtained the missing-mass spectrum of $^3\mathrm{He}(K^- ,n)$ and the exclusive analysis result of $^3\mathrm{He}(K^-,\Lambda p)n$ reaction. We have also examined not only the expected $K^-pp\rightarrow \Lambda p$ decay but also multi-nucleon absorption processes of in-flight $K^-$ by reconstructing the exclusive $^3\mathrm{He}(K^- ,\Lambda p)n$ channel. In this talk, we present the latest analysis results of the first physics data of J-PARC E15.