Processes concerning the number of neutrino types

The total number N_ν of neutrino types (νₑ, ν_μ, ν_τ, etc.) is involved in all neutral-current processes in which a νν pair is produced. We examine in detail three such processes: e⁺e^-→γνν, K⁺→π⁺νν, and KL→γνν. We find that e⁺e^-→γνν is especially suited for measuring N_ν, and that the experiment should be feasible at the colliding-beam machines PEP and PETRA.