A Search for the Decay $B^{-}\to K^{-} \nu \bar{\nu}$

We present a search for the rare flavour-changing neutral-current decay $B^{-}\to K^{-} \nu \bar{\nu}$ based on a sample of $(86.9 \pm 1.0) \times 10^{6}$ $\Upsilon (4S) \to$B\bar{B}$events collected by the BABAR experiment at the SLAC B-factory. Signal candidate events are selected by fully reconstructing a$B^+ \to \bar{D}^{0} X^+$decay, where$X^+$represents a combination of up to three charged pions or kaons and up to two$\pi^0$candidates. The charged tracks and calorimeter clusters not used in the$B^+$reconstruction are required to be compatible with a$B^{-}\to K^{-} \nu \bar{\nu}$decay. We observe a total of three signal candidate events with an expected background of$2.7 \pm 0.8$, resulting in a preliminary limit of$\mathcal{B}(B^{-}\to K^{-} \nu \bar{\nu}) < 1.05 \times 10^{-4}$at the 90$B^{-}\to K^{-} \nu \bar{\nu}$to give a limit of$\mathcal{B}(B^{-}\to K^{-} \nu \bar{\nu}) < 7.0 \times 10^{-5}$ at the 90% confidence level.