Measurement of Atmospheric Neutrino Flux Consistent with Tau Neutrino Appearance

A search for the appearance of tau neutrinos from {nu}{sub {mu}}{r_reversible}{nu}{sub {tau}} oscillations in the atmospheric neutrinos has been performed using 1489.2 days of atmospheric neutrino data from the Super-Kamiokande-I experiment. A best fit tau neutrino appearance signal of 138{+-}48(stat){sub -32}{sup +15}(syst) events is obtained with an expectation of 78{+-}26(syst). The hypothesis of no tau neutrino appearance is disfavored by 2.4 sigma.