Academic training less at CERN

Cosmic rays >2 GeV are isotropic + Gauss' Law + hypothesis of no oscillation => Φ_νμ(upward going)=Φ_νμ(downward going)
Instead, SuperKamiokande finds (for E_ν>1.3 GeV) a ratio of 0.54.
This is well described by a ν_μ->ν_τ oscillation with Δm²_atm~2*10^-3 eV² and almost maximal oscillation angle.

This can be tested with accelerator experiments, producing ν_μ from decay and observing disappearance (K2K, MINOS) or τ appearance (CERN-to-Gran Sasso).
K2K and MINOS so far confirm SuperKamiokande.