Tau neutrinos favored over sterile neutrinos in atmospheric muon neutrino oscillations.

The previously published atmospheric neutrino data did not distinguish whether muonneutrinos were oscillating into tau neutrinos or sterile neutrinos, as both hypotheses fitthe data. Using data recorded in 1100 live-days of the Super-Kamiokande detector, weuse three complementary data samples to study the difference in zenith angle distributiondue to neutral currents and matter effects. We find no evidence favoring sterile neutrinos,and reject the hypothesis at the 99% confidence level. On the other hand, we find thatoscillation between muon and tau neutrinos suffices to explain all the results in hand.I. INTRODUCTION