Improved Search for Muon-Neutrino to Electron-Neutrino Oscillations in MINOS

We report the results of a search for νₑ appearance in a ν_μ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of 8.2×10²⁰ protons on the NuMI target at Fermilab, we find that 2sin²(θ₂₃)sin²(2θ₁₃)<0.12(0.20) at 90% confidence level for δ=0 and the normal (inverted) neutrino mass hierarchy, with a best-fit of 2sin²(θ₂₃)sin²(2θ₁₃)=0.041_-0.031+0.047(0.079_-0.053+0.071). The θ₁₃=0 hypothesis is disfavored by the MINOS data at the 89% confidence level.