A Search for $\nu_{\mu} \to \nu_{\tau}$ Neutrino Oscillations in the $\tau \to \rho$ Decay Channel Using the NOMAD Detector

The standard model of particle physics includes three flavors of massless neutrinos. If neutrinos in fact have mass and non-zero mixing angles, one flavor may oscillate into another. A rich panoply of experiments have searched for this phenomenon using different types of neutrinos, from both man-made and extraterrestrial sources, over a wide range of energies, and employing a variety of detection techniques. Some recent experiments have claimed positive results in the search for neutrino oscillations. The NOMAD detector examined the neutrino beam at the CERN SPS for four years, from 1995 to 1998. These data are analyzed in a search for nm&rarr;nt oscillations in the t&rarr;r decay channel. The analysis employs a multidimensional kinematic likelihood function to separate signal events from backgrounds. The analysis finds no evidence of neutrino oscillations, and sets upper limits on the coupled parameters sin2 2&thetas; and &Delta;m 2 of sin2 2&thetas; < 8.79 × 10&ndash;3 for large &Delta;m2, and &Delta;m2 < 3.75 eV2/c4 at sin2 2&thetas; = 1.