Hitoshi Miyata

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.

Measurements of the inclusive jet cross section in photon-photon interactions at TRISTAN

Abstract We present cross section measurements for inclusive jet production in almost-real photon-photon interactions at TRISTAN using the AMY detector. The results are compared with leading-order QCD calculations for different parameterizations of the parton density in the photon.

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.

New limits on the masses of the selectron and photino

Abstract A study of e + e − annihilations into final states containing a single energetic photon with no accompanying particles is made at a center of mass energy of 57.8 GeV. The measured cross section is consistent with expectations from standard model processes and is used to set limits on the masses of the scalar electron and photino particles predicted by supersymmetry theories. If the photino is assumed to be massless, the 90% confidence level lower limit on the mass of the degenerate scalar electron is 65.5 GeV. If the results of all the single photon experiments are combined, this lower limit increases to 79.3 GeV.

Measurement of D-*+/- production in two-photon processes at TRISTAN

The inclusive cross section for the production of charmed D*(+/-) mesons in two-photon processes is measured with the AMY detector at the TRISTAN e(+)e(-) collider. D*(+/-) mesons ate identified from the distribution of charged-particle transverse momenta relative to the jet axis. A data sample corresponding to an integrated luminosity of 176 pb(-1) at a center-of-mass energy of 58 GeV is used to determine a cross section sigma(e(+)e(-) --> e(+)e(-)D*(+/-)X) = 270 +/- 49(stat) +/- 38(syst) pb. The results are compared with theoretical expectations based on the Vector Meson Dominance, direct quark-parton model, and resolved photon processes.

A measurement of Bose-Einstein correlations in e+e− annihilation at TRISTAN

Abstract Using e+e− annihilation events accumulated with the AMY detector at the TRISTAN collider, we have studied the Bose-Einstein correlations in the distributions of like-sign charged tracks. As reference samples we used the opposite-sign charged track pairs and mixed pairs, which are like-sign pairs synthesized from tracks belonging to different events. The results of the different reference samples give approximately 0.45 for the correlation strength and approximately 0.65 fm for the source size. Previous measurements of these parameters in e+e− annihilation at energies from CESR to LEP show remarkably flat dependence on s . Our results conform well with this picture.

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.