Search for dibaryon production in 4Hep interactions at intermediate energies

With the aid of the 2-m liquid-hydrogen bubble chamber constructed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow), 4Hep interactions are studied at primary alpha-particle momenta of 2.7 and 5 GeV/c (the respective kinetic energies of primary protons in the 4He rest frame are Tp=220 and 620 MeV). The effective-mass spectra of two nucleons from the reactions 4Hep → dppn and 4Hep → pppnn are analyzed. The effective-mass spectrum of the two-proton system produced in the quasielastic-charge-exchange reaction p4He → nF(pp)d at Tp=620 MeV (here, nF stands for the fast neutron in the 4He rest frame) shows a narrow peak, which is indicative of the existence of a dibaryon whose mass and width are M2p=2008±13 MeV and Γ2p=0±5 MeV, respectively. In the mass spectra of the two-proton system from the reactions p4He → nF(pp)d and p4He → pF(pp)(nn), narrow threshold peaks are also found at a mass of M2p⋍1878–1879 MeV.