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 $2{sin}^2({\theta }_{23}){sin}^2(2{\theta }_{13})={0.041}_{-0.031}^{+0.047}({0.079}_{-0.053}^{+0.071})$. The ${\theta }_{13}=0$ hypothesis is disfavored by the MINOS data at the 89% confidence level.

• Received 29 July 2011

DOI:https://doi.org/10.1103/PhysRevLett.107.181802