Improved search for muon-neutrino to electron-neutrino oscillations in MINOS

We report the results of a search for ${\nu }_e$ appearance in a ${\nu }_{\mu }$ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of $8.2\times {10}^{20}$ protons on the NuMI target at Fermilab, we find that $2{\sin }^2({\theta }_{23}){\sin }^2(2{\theta }_{13})<0.12(0.20)$ at 90% confidence level for $\delta =0$ and the normal (inverted) neutrino mass hierarchy, with a best fit of $2\sin^2(\theta_{23})\sin^2(2\theta_{13}),\mathord{=},0.041^{+0.047}{-0.031}
(0.079^{+0.071}{-0.053})$\mathrm{.}The$\theta_{13}\mathord{=}0$ hypothesis is disfavored by the MINOS data at the 89% confidence level.