Search for the Decay $B^{+}\to K^{+}\nu \overline{\nu }$

We search for the rare flavor-changing neutral-current decay $B^{+}\to K^{+}\nu \overline{\nu }$ in a data sample of $82{\mathrm{fb}}^{-1}$ collected with the BABAR detector at the PEP-II $B$-factory. Signal events are selected by examining the properties of the system recoiling against either a reconstructed hadronic or semileptonic charged-$B$ decay. Using these two independent samples we obtain a combined limit of $\mathcal{B}(B^{+}\to K^{+}\nu \overline{\nu })<5.2\times {10}^{-5}$ at the 90% confidence level. In addition, by selecting for pions rather than kaons, we obtain a limit of $\mathcal{B}(B^{+}\to {\pi }^{+}\nu \overline{\nu })<1.0\times {10}^{-4}$ using only the hadronic $B$ reconstruction method.

Figure 1

(a) The $D^0$ mass distribution for $D^0\to K^{-}{\pi }^{+}$ decays used for $B_{\mathrm{sl}}^{-}$ reconstruction. Data are shown as points and the total background MC simulation is shown as a solid histogram. (b) The $m_{\mathrm{ES}}$ distribution of $B_{\mathrm{had}}^{-}$ events for data (points) and $B\overline{B}$ MC simulation (solid histogram). Continuum background has been subtracted from the on-resonance data using off-resonance data. The hatched histogram represents the estimated combinatorial background from $B\overline{B}$ decays.

Figure 2

The $E_{\mathrm{extra}}$ distribution for $B^{+}\to K^{+}\nu \overline{\nu }$ $B_{\mathrm{had}}^{-}$ (left) and $B_{\mathrm{sl}}^{-}$ (right) events. Events are required to have a reconstructed $B^{-}$ and exactly one additional track which has been identified as a kaon. No other signal-selection cuts have been applied. The data and background MC samples are represented by the points with error bars and solid histograms, respectively. The dotted line indicates the expected $B^{+}\to K^{+}\nu \overline{\nu }$ signal distribution from MC simulation.

Figure 3

The $p_K$ distribution for (a) $B_{\mathrm{had}}^{-}$ and (b) $B_{\mathrm{sl}}^{-}$ events after applying the full $B^{+}\to K^{+}\nu \overline{\nu }$ selection except for the $p_K>1.25\mathrm{GeV}/c$ requirement. The dotted line indicates the expected signal distribution from MC simulation. The data are represented by the points. The expected background distributions obtained from MC simulation are also plotted (solid histograms) although it should be noted that estimates of nonpeaking backgrounds are obtained directly from data and hence differ slightly from the MC estimates shown here.

Figure 4

The $E_{\mathrm{extra}}$ (a) and $p_{\pi }$ (b) distributions for $B^{+}\to {\pi }^{+}\nu \overline{\nu }$ in the $B_{\mathrm{had}}^{-}$ sample. Events shown in the $E_{\mathrm{extra}}$ distribution are required to have a reconstructed $B^{-}$ and exactly one additional track satisfying the pion-selection requirements. The $p_{\pi }$ distribution has all signal-selection requirements applied other than the $p_{\pi }$ cut. The data and background MC samples are represented by the points and the solid histogram, respectively. The dotted line indicates the expected signal distribution from MC simulation.