High Statistics Search for ν_μ(ν̅ _μ)→ν_e(ν̅ _e) Oscillations in the Small Mixing Angle Regime

Limits on ν_μ(ν̅ _μ)→ν_e(ν̅ _e) oscillations based on a statistical separation of ν_eN charged current interactions in the CCFR detector at Fermilab are presented. Neutrino energies range from 30 to 600 GeV with a mean of 140 GeV, and ν_μ flight lengths vary from 0.9 to 1.4 km. The result excludes oscillations in the region with sin²2α>1.8×10^-3 for large Δm²(>1000eV²) and Δm²>1.6eV² for sin²2α = 1. This result is the most stringent limit to date for Δm²>25eV² and it excludes the high Δm² oscillation region favored by the LSND experiment. The ν_μ-to- ν_e cross-section ratio was measured as a test of ν_μ(ν̅ _μ)↔ν_e(ν̅ _e) universality to be 1.026±0.025(stat)±0.049(syst).