STUDY OF INVISIBLE NUCLEON DECAY, N-]NU-NU(NU)OVER-BAR, AND A FORBIDDEN NUCLEAR TRANSITION IN THE KAMIOKANDE DETECTOR

A search was made for anomalous gamma-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 --> nu(mu)nu(mu)nu(mu)BAR, n --> nu(e)nu(e)nu(e)BAR and n --> nu(tau)nu(tau)nu(tau)BAR. A lower limit on the partial life time tau(B) is given by tau(B)/Br(gamma) = 1.8 X 10(31) yr(90% CL), where Br(gamma) = GAMMA(gamma)/GAMMA(tot) is the branching fraction of the gamma-decay to the particle emission of the deexcitation of O-15*. The life time limit becomes tau(B) = 4.9 X 10(26) yr (90% CL) for a conservative estimate of Br(gamma) = 2.7 X 10(-5) assuming a nuclear single particle model. The result was also used for studying forbidden transitions in the O-16 nucleus. The limit for the relative strength of the forbidden transition to the normal transition is < 2.3 X 10(-57) (90% CL).