A more sensitive search for νμ→ντ oscillations in NOMAD

Abstract With additional data and improved algorithms, we have enhanced the sensitivity of our appearance search for ν μ → ν τ oscillations in the NOMAD detector in the CERN-SPS wide-band neutrino beam. The search uses kinematic criteria to identify ν τ charged current interactions followed by decay of the τ − to one of several decay modes. Our “blind” analyses of deep-inelastic scattering data taken in 1996 and 1997, combined with consistent reanalyses of previously reported 1995 data, yield no oscillation signal. For the two-family oscillation scenario, we present the contour outlining a 90% C.L. confidence region in the sin 2 2 θ μτ – Δm 2 plane. At large Δm 2 , the confidence region includes sin 2 2 θ μτ −3 (a limit 3.5 times more stringent than in our previous publication), while at sin 2 2 θ μτ =1, the confidence region includes Δm 2 2 / c 4 .