Search for electron antineutrino appearance at the deltam(2) approximately 1 eV(2) Scale

The MiniBooNE Collaboration reports initial results from a search for nu(mu)--nu(e) oscillations. A signal-blind analysis was performed using a data sample corresponding to 3.39x10(20) protons on target. The data are consistent with background prediction across the full range of neutrino energy reconstructed assuming quasielastic scattering, 200E(nu)(QE)3000 MeV: 144 electronlike events have been observed in this energy range, compared to an expectation of 139.2+/-17.6 events. No significant excess of events has been observed, both at low energy, 200-475 MeV, and at high energy, 475-1250 MeV. The data are inconclusive with respect to antineutrino oscillations suggested by data from the Liquid Scintillator Neutrino Detector at Los Alamos National Laboratory.