Study of the Elementary (K-, n) Reactions to Search for the (K)over-barNN Bound State via the He-3 (K-, n) Reaction at J-PARC

We have searched for the simplest kaonic nuclear state, (K) over tilde NN, using the in-flight He-3 (K- ,n) reaction at the J-PARC hadron experimental facility. In the semi-inclusive neutron missing-mass spectrum at theta(lab)(n) = 0, an excess of yield was observed just below the K- pp mass-threshold, which cannot be explained by any elementary reactions [PTEP 2015, 061D01]. To understand the missing-mass spectrum of He-3(K-,n)X, we investigated the elementary (K-, n) reactions using hydrogen and deuterium targets. The p(K- ,n)X missing-mass spectrum was well described by the charge-exchange reaction. flowever, in the d(K-,n)X spectrum, we observed an excess of yield just below the K(-)p mass-threshold, which was similar to that in the He-3(K-,n)X spectrum.