Search for Flavor-Changing Neutral Current and Lepton-Flavor Violating Decays of $D^0\to l^{+}{l}^{-}$

We report on a search for the flavor-changing neutral current decays $D^0\to e^{+}{e}^{-}$ and $D^0\to {\mu }^{+}{\mu }^{-}$, and the lepton-flavor violating decay $D^0\to e^{\pm }{\mu }^{\mp }$. The measurement is based on $122{\mathrm{f}\mathrm{b}}^{-1}$ of data collected by the BABAR detector at the SLAC PEP-II asymmetric $e^{+}{e}^{-}$ collider. No evidence is found for any of the decays. The upper limits on the branching fractions, at the 90% confidence level, are $1.2\times {10}^{-6}$ for $D^0\to e^{+}{e}^{-}$, $1.3\times {10}^{-6}$ for $D^0\to {\mu }^{+}{\mu }^{-}$, and $8.1\times {10}^{-7}$ for $D^0\to e^{\pm }{\mu }^{\mp }$.

Figure 1

The dilepton invariant mass distribution for each decay mode. The dashed lines indicate the optimized signal mass window.