A Measurement of Atmospheric Neutrino Flux Consistent with Tau Neutrino Appearance

A search for the appearance of tau neutrinos from \mutau 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 $\pm$ 48 (stat.) $^{+15}_{-32}$ (sys.) events is obtained with an expectation of 78 $\pm$ 26 (sys.). The hypothesis of no tau neutrino appearance is disfavored by 2.4 sigma.