E. Kodera

Observation of a small atmospheric vμ/ve ratio in Kamiokande

Abstract Results are presented of the observation of atmospheric neutrino interactions in the Kamiokande detector in an exposure of 4.92 kt yr. The observed ratio of single ring μ-events to e-events ( μ e ) data ( μ e ) MC = 0.60 +007 −0.06 ( stat. ) ± 0.05 ( syst. ) suggests that the atmospheric v μ /v e ratio is smaller than expected. The implications of these results for neutrino oscillations are discussed.

Search for neutralino dark matter in Kamiokande

Abstract A search has been made for upward-going muons in the Kamiokande detector as a possible signal from neutralino dark matter captured in the earth. We found the upward-going muon flux from the earth is consistent with that produced by the atmospheric neutrinos. Assuming the galactic halo contains neutralino dark matter, this result provides limits on the neutralino mass in the region 30–80 GeV and gives stringent constraints on the allowed regions of the parameter space in the framework of the minimal supersymmetric standard model.

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).

A limit on massive neutrino dark matter from Kamiokande

Abstract We have searched for possible high-energy neutrino signals expected from massive neutrino dark matter captured by the earth and the sun, by making use of upward-going muon samples collected in the seven years of operation of the Kamiokande detector. No excess of events was found from the earth or the sun, thus giving an excluded mass range of Dirac-(Majorana-) type neutrinos, 6 (24) ⩽ m ν ⩽ several hundred GeV, as the dark matter which consitutes the halo of the galaxy. The upper bounds extend to a mass range never before analyzed in previous indirect searches.

Survey of atmospheric neutrino data and implications for neutrino mass and mixing

Abstract A detailed comparison is made of the atmospheric neutrino results obtained by the Frejus, IMB-3, and Kamiokande detectors. The implications of these results for vacuum neutrino oscillations are presented, and juxtaposed with the results for matter neutrino oscillations from the solar neutrino data.

A limit on spontaneous R parity breaking from Kamiokande

Abstract If R parity is not an exact symmetry in supersymmetric theories, the lightest supersymmetric partner, most favorably the neutralino, would not be stable, but may decay to produce energetic neutrinos. We show that a lack of excess neutrino events above the atmospheric neutrino background, obtained from upward-going muon data in Kamiokande, places a severe constraint on models of R parity breaking if the neutralino is a dark-matter particle.