Study of the elementary (K−, n) reactions to search for the K¯NN bound state via the 3He (K−, n) reaction at J-PARC

We have searched for the simplest kaonic nuclear state, KNN, using the in-flight 3He (K-, n) reaction at the J-PARChadron experimental facility. In the semi-inclusive neutron missing- mass spectrumat θnlab=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 spectrumof 3He (K-, n) X, we investigated the elementary (K-, n) reactions using hydrogen and deuterium targets. The p (K-, n) X missing- mass spectrumwas well described by the charge-exchange reaction. However, 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 3He (K-, n) X spectrum. (Less)