Study of invisible nucleon decay, N ---> neutrino neutrino anti-neutrino, and a forbidden nuclear transition in the Kamiokande detector

Abstract A search was made for anomalous γ-rays in the energy range 19 and 50 MeV in the large underground water Cherenkov detector Kamiokande. We found no significant excess above the known backgrounds. The result was used to set a limit on invisible nucleon decay through n→ν μ ν μ ν μ , n→ν e ν e ν e and n→ν τ ν τ ν τ . A lower limit on the partial life time τ B is given by τ B /Br( γ )=1.8×10 31 yr(90% CL), where Br( γ )= Γ γ / Γ tot is the branching fraction of the γ-decay to the particle emission of the deexcitation of 15 O ∗ . The life time limit becomes τ B =4.9×10 26 yr(90% CL) for a conservative estimate of Br( γ )=2.7×10 −5 assuming a nuclear single particle model. The result was also used for studying forbidden transitions in the 16 O nucleus. The limit for the relative strength of the forbidden transition to the normal transition is −57 (90% CL).