A global analysis of the atmospheric neutrino data

The recent observations of atmospheric nu events from the Super-Kamiokande experiment are compatible with two-flavor oscillations in the nu(mu)<---->n u(tau) channel ("standard" interpretation). Among the possible deviations f rom this standard picture, we investigate two cases: (1) three-flavor oscil lations and (2) a specific solution without oscillations (namely, neutrino decay). While the first solution appears perfectly viable, provided that th e 3 nu oscillations occur dominantly in the nu(mu)<---->nu(tau) channel and subdominantly in the nu(mu)<---->nu(e) channel, the second is shown to be incompatible with the data. The derivation of such results is based on an u pdated analysis, including the latest 45 kTy data sample from Super-Kamioka nde. A comparison with our previous results, based on 33 kTy data, shows th at the oscillation evidence is strengthened, and that the neutrino mass-mix ing parameters are constrained in smaller ranges. (C) 2000 Elsevier Science B.V. All rights reserved.