We present an analysis of atmospheric neutrino data from a 33.0 kton yr (535-day) exposure of the Super-Kamiokande detector. The data exhibit a zenith angle dependent deficit of muon neutrinos which is inconsistent with expectations based on calculations of the atmospheric neutrino flux. Experimental biases and uncertainties in the prediction of neutrino fluxes and cross sections are unable to explain our observation. The data are consistent, however, with two-flavor n m $ n t oscillations with sin 2 2u . Atmospheric neutrinos are produced as decay products in hadronic showers resulting from collisions of cosmic rays with nuclei in the upper atmosphere. Production of electron and muon neutrinos is dominated by the processes p 1 ! m 1 1 n m followed by m 1 ! e 1 1 n m 1 n e (and their charge conjugates) giving an expected ratio 1562 0031-9007͞98͞81(8)͞1562(6)$15.00

A neutrino burst was observed in the Kamiokande II detector on 23 February 1987, 7:35:35UT (+ 1 min) during a time interval of 13 sec. The signal consisted of eleven electron events of energy 7.5 to 36 MeV, of which the first two point back to the Large Magellanic Cloud with angles 18~18 and 15 + 27

Solar neutrino measurements from 1258 days of data from the Super-Kamiokande detector are presented [? ]. The measurements are based on recoil electrons in the energy range 5.0-20.0 MeV. The measured solar neutrino flux is 2.32 ± 0.03 (stat.) +0.08 −0.07 (sys.) ×10 6 cm −2 s −1 , which is 45.1 ± 0.5 (stat.) +1.6 −1.4 (sys.)% of that predicted by the BP2000 SSM. The day vs night flux asymmetry (Φn − Φ d )/Φaverage is 0.033 ± 0.022 (stat.) +0.013 −0.012 (sys.). The recoil electron energy spectrum is consistent with no spectral distortion (χ 2 /d.o.f. = 19.0/18). The seasonal variation of the flux is consistent with that expected from the eccentricity of the Earth's orbit (χ 2 /d.o.f. = 3.7/7). For the hep neutrino flux, we set a 90% C.L. upper limit of 40 × 10 3 cm −2 s −1 , which is 4.3 times the BP2000 SSM prediction.22 This preprint is almost identical to the report submitted to Physical Review Letter. We have added to this preprint a few tables of

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