Y. Nagashima

Atmospheric muon-neutrino / electron-neutrino ratio in the multiGeV energy range

Abstract Data from the Kamiokande detector were used to study the atmospheric (v μ + v μ ) (v e + v e ) ratio in the multi-GeV energy range. The observed ratio of μ-like to e-like events relative to the calculated ratio, ( μ /e) data /( μ /e) MC = 0.57 -0.07 +0.08 ± 0.07, suggests that the atmospheric (v μ + v μ ) (v e + v e ) ratio is smaller than expected for these neutrino energies. Also studied was the zenith-angle dependence of the above ratio. Results of an analysis of neutrino oscillations are presented.

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.

Measurement of the flux and zenith angle distribution of upward through going muons in Kamiokande II + III

The flux of upward through-going muons of minimum (mean) threshold energy > 1.6 (3.0) GeV is measured, based on a total of 372 events observed by the Kamiokande II+III detector during 2456 detector live days. The observed muon flux was (1.94+-0.10(stat.)+0.07-0.06(sys.))*10^-13 /cm^2/s/sr, which is compared to an expected value of (2.46+-0.54(theo.))*10^-13/cm^2/s/sr. The observation is in agreement with the prediction within the errors. The zenith angle dependence of the observed upward through-going muons supports the previous indication of neutrino oscillations made by Kamiokande using sub- and multi-GeV atmospheric neutrino events.

Search for a rare decay mode K+ → π+νv and axion

Abstract Using stopped kaons, rare decay modes K + → π + ν v and K + → π + a 0 is the light pseudoscalar meson (axion), have been measured. The upper bound of the branching ratio was found to be 1.4 × 10 −7 for K + → π + ν v and 3.8 × 10 −8 for K + → π + a 0 .

Search for a Rare Decay Mode K+ ---> pi+ Neutrino anti-neutrino and Axion

Abstract Using stopped kaons, rare decay modes K + → π + ν v and K + → π + a 0 is the light pseudoscalar meson (axion), have been measured. The upper bound of the branching ratio was found to be 1.4 × 10 −7 for K + → π + ν v and 3.8 × 10 −8 for K + → π + a 0 .

A study of the axial-vector form factor and second-class currents in antineutrino quasielastic scattering

Abstract The antineutrino quasielastic reaction ν μm p →μ + n has been studied in the Q 2 range up to 1.0 (GeV/ c ) 2 at the Brookhaven AGS. The value of the axial vector mass M A in the dipole parametrization of the from factor was determined from the shape of the Q 2 distribution to be 1.09±0.03±0.02 GeV/ c 2 . A search for second-class currents was also conducted. No significant effect was found.

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.

Experimental limits on nucleon lifetime for lepton+meson decay modes

Abstract We have searched for nucleon decay signals using data from the KAMIOKANDE-II detector. No evidence for nucleon decay has been found. Limits on the nucleon partial lifetime for various decay modes are obtained combining KAMIOKANDE-I and -II data (3.76 kt yr in total). The background subtracted limits at 90% CL range from 0.1×1032yr to 2.6×1032yr depending on the decay modes. For the decay modes p→e+π0, p→ v K+ and n→ v K0, the limits are 2.6×1032yr, 1.0×1032yr and 0.9×1032yr, respectively.

An indium phosphide solid state detector: A possible low energy gamma and neutrino detector

Abstract An indium phosphide (InP) diode has been developed which could be used as a low energy γ-ray detector. The p-n junction was formed by diffusing Zn into a layer grown by the liquid phase epitaxial process. The detector has been operated at room temperature and spectrum responses for α-particles and γ-rays have been measured. The resolution obtained was 10% (FWHM) for 2.2 MeV α-particles. This is the first report on the p-n junction InP solid state detector having an ability to detect low energy γ-rays.

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).