Structure near the threshold in the in-flight He reaction

Sada, Yuta*; Tanida, Kiyoshi   ; J-PARC E15 Collaboration*; 69 of others*

To search for an di-baryonic state which decays to , the He reaction was studied at 1.0 GeV/. Unobserved neutrons were kinematically identified from the missing mass of the He reaction in order to have a large acceptance for the final state. The observed events, distributed widely over the kinematically allowed region of the Dalitz plot, establish that the major component comes from a three-nucleon absorption process. A concentration of events at a specific neutron kinetic energy was observed in a region of low momentum transfer to the . To account for the observed peak structure, the simplest -wave pole was assumed to exist in the reaction channel, having a Breit-Wigner form in energy and with a Gaussian form factor. A minimum method was applied to deduce its mass, MeV/, and decay width, MeV/, respectively. The form factor parameter MeV/ implies that the range of the interaction is about 0.5 fm.