A more sensitive search for νμ→ντ oscillations in NOMAD

With additional data and improved algorithms, we have enhanced the sensitivity of our appearance search for vμ → vτ oscillations in the NOMAD detector in the CERN-SPS wide-band neutrino beam. The search uses kinematic criteria to identify vτ 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 sin22θμτ-Δm2plane. At large Δm2, the confidence region includes sin22θμτ <1.2 × 10-3 (a limit 3.5 times more stringent than in our previous publication), while at sin22θμτ = 1, the confidence region includes Δm2 < 1.2 eV2/c4. © 1999 Published by Elsevier Science B.V. All rights reserved.