Search for $\mathit{B}\to \tau \nu$ and $\mathit{B}\to \mathit{K}\nu \overline{\nu }$

We report results of a search for $B\to \tau \nu$ in a sample of $9.7\times {10}^6$ charged $B$ meson decays. We exclusively reconstruct the companion $\overline{B}$ decay to suppress background. We set an upper limit on the branching fraction $B(B\to \tau \nu )<8.4\mathrm{}\times {10}^{-4\mathrm{}}$ at $90\%$ confidence level. We also establish $B(B^{\pm }\to K^{\pm }\nu \overline{\nu })<2.4\mathrm{}\times {10}^{-4\mathrm{}}$ at $90\%$ confidence level.