Seeking and investigating isospin-two narrow dibaryon resonances in neutron-proton interactions at P n =5.20±0.13 Gev/c

The results are presented that are obtained from searches for and an investigation of isospin-two narrow resonances in the effective-mass spectrum of ppπ+ combinations originating from the reaction np → ppπ+π−π− induced by P n =5.20±0.13 GeV/c neutrons. Data subjected to our analysis come from the 1-m hydrogen bubble chamber installed at the Laboratory for High Energies, Joint Institute for Nuclear Research (Dubna), and exposed to a beam of quasimonochromatic neutrons. Narrow structures in the effective-mass spectrum of ppπ+ combinations are found at 2175, 2221, 2321, 2398, 2471, 2525, 2596, and 2709 MeV/c2. The experimental widths of the resonances are determined primarily by the instrumental resolution. The branching fractions for various channels through which the 2596-MeV/c2 resonance decays are determined to be (83±23)% for the Δ 33 ++ p channel, (10±3)% for the (BB) 2095 ++ π+ channel, and (7 −7 +15 for the ppπ+ channel; here, (BB) 2095 ++ is a dibaryon in the two-proton system with a mass around 2095 MeV/c2. A qualitative analysis of the spins of the 2596-and 2709-MeV/c2 resonances is performed.