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

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The results of a comprehensive analysis of existing data on the weak neutral current and the W and Z masses are presented. The principal results are the following. (a) There is no evidence for any deviation from the standard model. (b) A global fit to all data yields sin 0~= 1 -Mgr /Mz =0.230+0.0048, where this error and all others given here include full statistical, systematic, and theoretical uncertainties (computed assuming three fermion families, m, & 100 GeV, and MH & 1 TeV). (c) Allowing p=M~/(Mz cos'0~) as well as sin'0~to vary one obtains sin 0~=0.229+0.0064 and p =0.998+0.0086. This implies 90%%uo-confidence-level (C.L.) upper limits of 0.047 and 0.081 for the vacuum expectation values (relative to those of Higgs doublets) for Higgs triplets with weak hypercharge of 0 and +1, respectively. (d) The parameter6~=drhs (1 -Ar)/sin'0, which is a measure of the radiative corrections relating deepinelastic neutrino scattering, the 8' and Z masses, and muon decay, is determined to be 0. 112+0.037. This is consistent with the value 5~--0. 106 expected for m, =45 GeV and MH --100 GeV and establishes the existence of radiative corrections at the 3o. level. (e) The radiative corrections are sensitive to isospin breaking associated with a large m, . Assuming no deviation from the standard model, consistency of the various reactions requires m«180 GeV at 90%%uo C.L. for M& & 100 GeV, with a slightly weaker limit for larger MH. Similar results hold for the mass splittings between fourth-generation quarks or leptons. (f) Most of the parameters in modelindependent fits to vq, ve, eq, and e+e processes are now determined uniquely and precisely. (g) Limits are given on the masses and mixing angles of additional Z bosons expected in popular models. For theoretically expected coupling constants one finds that the neutral-current constraints are usually more stringent than the direct-production limits from the CERN SppS collider, but nevertheless masses as low as 120 -300 GeV are typically allowed. (h) The implications of these results for grand unification are discussed. sin 0~is )2.5 standard deviations above the prediction of minimal SU(5) and similar models for all m, . It is closer to the prediction of simple supersymmetric grand unified theories but is still somewhat low. (i) The dominant theoretical uncertainty (the charm-quark threshold in deep-inelastic charged-current scattering) is considered in some detail.

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