Indications on neutrino oscillations parameters from initial K 2 K and current SK data

We briefly discuss the impact of initial data from the KEK-to-Kamioka (K2K) neutrino experiment on the ν µ → ν τ oscillation parameters (m 2 , tan 2 ψ) currently indicated by the Super-Kamiokande (SK) atmospheric neutrino experiment. After showing the very good agreement between K2K and SK, we combine the two separate pieces of information. We find that the 99% C.L. range for m 2 allowed by SK only, m 2 ∈ [1.3, 5.6] × 10 −3 eV 2 , is reduced to [1.5, 4.8] × 10 −3 eV 2 by including K2K data. By halving the uncertainties of the K2K total rate (with central value unchanged), the m 2 range would be ulteriorly reduced to [1.8, 4.0] × 10 −3 eV 2. Such information appears to be already useful in planning (very) long baseline neutrino oscillation experiments.