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. W e 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 parti cle 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(g amma) = 2.7 X 10(-5) assuming a nuclear single particle model. The res ult was also used for studying forbidden transitions in the O-16 nucle us. The limit for the relative strength of the forbidden transition to the normal transition is < 2.3 X 10(-57) (90% CL).