New Results on Electron Neutrino Appearance in MINOS

Neutrino oscillation is now an established phenomenon, thanks to a variety of experiments [1, 2, 3, 4, 5, 6, 7] which have probed various apparent anomalies in expected neutrino spectra from the sun, atmosphere, nuclear reactors, and accelerator-based beams. The three weak eigenstates - v_e, v_μ, v_r - are related to the three mass eigenstates - v_1, v-2, v_3 - via the PMNS (for Pontecorvo, Maki, Nakagawa, and Sakata) matrix, a unitary mixing matrix U parametrized by three mixing angles - θ_(12), θ_(13), θ_(23) - and three CP-violating phases - δ, ɑ_1, ɑ_2 [8]. No hints exist yet as to the value of δ, and oscillation experiments are not sensitive to the latter two CP-violating phases, which are nonzero only if neutrinos are their own antiparticles (i.e., Majorana particles). So far, two of the mixing angles, θ_(12) and θ_(23), have been measured [1, 4, 6] and are large. The value of θ_(13), on the other hand, appears to be quite small. It was first significantly constrained by the CHOOZ experiment in 1999 [9]; the result is shown in Fig.1. These proceedings report the latest improvements on this constraint by the MINOS experiment and survey the future of research in this area.