Results from the NOMAD experiment

Abstract

The NOMAD experiment has sought ν_μ ↔ ν_τ oscillations by looking for the emergence of τ⁻ in events from the CERN SPS neutrino beam. With some improvements in the techniques of analysis in relation to the results published previously and with the inclusion of data from the 1998 run, no evidence for the oscillations has been found, which results in an updated limit on the oscillation probability [P(ν_μ → ν_τ) < 0.5 × 10⁻³ at a 90% C.L.]. The corresponding limit on the oscillation mixing angle is given by sin²2θ_μτ < 1.0 × 10⁻³ for large Δm ². By using a 1% contamination of ν_e in the neutrino beam, we can also rule out ν _e ↔ ν_τ oscillations and constrain the probability of the relevant transition as P(ν _e → ν_τ) < 3 × 10⁻² at a 90% C.L. (sin²2θ _eτ < 6 × 10⁻² at large Δm ²).