Initial Results for Electron-Neutrino Appearance in MINOS

Abstract

MINOS is a long baseline neutrino oscillation experiment designed to make precision measurements of the neutrino mixing parameters associated with the atmospheric neutrino mass splitting. Using a neutrino beam from the Main Injector (NuMI) facility at Fermilab, it compares the neutrino energy spectrum for neutrino interactions observed in two large detectors located at Fermilab and in the Soudan mine in northern Minnesota at a distance of 735km. We describe initial results for electron neutrino appearance in MINOS after two years of data-taking. We observe 35 events in the Far Detector with a background prediction of $27\pm 5 {\rm (stat.)} \pm 2 {\rm (syst.)$ based on the measurement in the Near Detector. The 1.5$\sigma$ excess of events can be interpreted in terms of $\nu_{\mu}$ to $\nu_{e}$ oscillations. At 90% CL we obtain an upper limit range of $\sin^2(2\theta_{13})< 0.28-0.34$ for the normal neutrino mass hierarchy and $\sin^2(2\theta_{13})< 0.36-0.42$ for the inverted hierarchy depending upon $\delta_{CP}$.