Latest Results from K2k A

The possible existence of neutrino masses is the first signal beyond the standard model, which suggests grand unification. The KEK-to-Kamioka long-baseline neutrino experiment (K2K) 1 is motivated by the atmospheric neutrino anomaly found by the Kamiokande experiment . One possible explanation of the anomaly is neutrino oscillation. Later, the Super–Kamiokande (SK) group confirmed the deficit of upward-going atmospheric νμ, and announced evidence for the oscillation of atmospheric neutrinos 3 with a difference of the squared masses, ∆m ∼ 3× 10eV, and the mixing parameter, sin2θ ∼ 1. For a neutrino energy of Eν(GeV) and a flight length of L(km), the oscillation probability is expressed by the following formula in a two-flavor approximation: