Search for Dibaryon Production in ~4Hep Interactions at Intermediate Energies

摘要

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 T_p = 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 p~4Hep → n_F(pp)d at T_p = 620 MeV (here, n_F stands for the fast neutron in the ~4Hep rest frame) shows a narrow peak, which is indicative of the existence of a dibaryon whose mass and width are M_(2p) = 2008 ± 13 MeV and Γ_(2p) = 20 ± 5 MeV respectively. In the mass spectra of the two-proton system from the reactions p~4He → n_F(pp)d and p~4He → p_F (pp)(nn), narrow threshold peaks are also found at a mass of M_(2p) approx= 1878-1879 MeV.