Search for the deeply bound K- pp state from the semi-inclusive forward-neutron spectrum in the in-flight K- reaction on helium-3

Abstract

An experiment to search for the K- pp bound state was performed via the in-flight 3He(K-, n) reaction using 5.3 × 109 kaons at 1GeV/c at the J-PARC hadron experimental facility. In the semi-inclusive neutron missing-mass spectrum at θnlab = 0°, no significant peak was observed in the region corresponding to K- pp binding energy larger than 80MeV, where a bump structure has been reported in the Λp final state in different reactions. Assuming the state to be isotropically decaying into Λp, mass-dependent upper limits on the production cross section were determined to be 30-180, 70-250, and 100-270 μb/sr, for the natural widths of 20, 60, and 100MeV, respectively, at 95% confidence level.