Atmospheric neutrinos and neutrino oscillations

Atmospheric neutrinos are produced by the interaction of primary cosmic rays in the upper atmosphere. Their measurement with large underground detectors has given results that are inconsistent with predictions based on the Minimal Standard Model. The nu(e) and (nu) over bar (e) fluxes, within errors, are compatible with the standard prediction, while the nu(mu) and (nu) over bar (mu) fluxes show a significant suppression. The dependence of the suppression on the neutrino energy and direction (path-length) can be accurately described assuming the existence of two flavor v(mu) <-> nu(tau) oscillations with parameters in the (90% CL) allowed interval: 1.5 < vertical bar Delta m(2)vertical bar /(10(-3) eV(2)) < 3.4 and sin(2) 20 >= 0.92. Various features of neutrino oscillations have been studied based oil these data.