COMPARISON OF NU(MU)[--]NU(TAU) AND NU(MU)[--]NU(S) OSCILLATIONS AS SOLUTIONS OF THE ATMOSPHERIC NEUTRINO PROBLEM - ART. NO. 073005

The simplest explanation for the atmospheric neutrino anomaly is the t ransition of muon neutrinos and antineutrinos into states of different flavor. Data from the reactor experiment CHOOZ, and the measurement o f the energy and angle distribution of electronlike events at Super-Ka miokande put strong constraints on nu(mu)-nu(e) mixing, but the transi tions nu(mu) --> nu(tau) and nu(mu) --> nu(s) are viable possibilities . If the muon neutrinos are mixed with a singlet sterile state, the en ergy and zenith angle dependence of the oscillation probability is mod ified by matter effects that are important for E-nu/\Delta m(2)\greate r than or similar to 10(3) GeV/eV(2). We confront the theoretical pred ictions with existing data on contained events and neutrino-induced up ward-going muons. [S0556-2821(98)00319-1]