Up-Down Asymmetry of Neutral Current Events as a Diagnostic for Nu_mu -   Nu-st Versus Nu_mu- Nu_tau Oscillations
  We show that the asymmetry in the neutral current events (e.g. Nu N -> Nu N pi^0) can be used to discriminate between Nu_mu - Nu_tau and Nu_mu - Nu_st mixing as being responsible for the atmospheric neutrino anomaly. Specifically, A_N vanishes for Nu_mu - Nu_tau mixing and is about 2/3 A_mu for Nu_mu - Nu_st mixing. 
John G. Learned, Sandip Pakvasa and J. L. Stone