6533b7d1fe1ef96bd125d965

RESEARCH PRODUCT

A more sensitive search for νμ→ντ oscillations in NOMAD

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With additional data and improved algorithms, we have enhanced the sensitivity of our appearance search for $\numunutau$ oscillations in the NOMAD detector in the CERN-SPS wide-band neutrino beam. The search uses kinematic criteria to identify $\nutau$ charged current interactions followed by decay of the $\tau^-$ 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 $\sin^22\theta_{\mu \tau} - \Delta m^2$ plane. At large $\Delta m^2$, the confidence region includes $\sin^22\theta_{\mu\tau}\ \ 1.2\times10^{-3}$ (a limit 3.5 times more stringent than in our previous publication), while at $\sin^22\theta_{\mu \tau}=1$, the confidence region includes $\Delta m^2 1.2$ eV$^2$/$c^4$.