Searches for rare or forbidden semileptonic charm decays

Abstract

We present searches for rare or forbidden charm decays of the form ${X}_{c}^{+}\ensuremath{\rightarrow}{h}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\ell}}^{\ensuremath{\mp}}{\ensuremath{\ell}}^{(\ensuremath{'})+}$, where ${X}_{c}^{+}$ is a charm hadron (${D}^{+}$, ${D}_{s}^{+}$, or ${\ensuremath{\Lambda}}_{c}^{+}$), ${h}^{\ifmmode\pm\else\textpm\fi{}}$ is a pion, kaon, or proton, and ${\ensuremath{\ell}}^{(\ensuremath{'})\ifmmode\pm\else\textpm\fi{}}$ is an electron or muon. The analysis is based on $384\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of ${e}^{+}{e}^{\ensuremath{-}}$ annihilation data collected at or close to the $\ensuremath{\Upsilon}(4S)$ resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the 35 decay modes that are investigated. We establish 90% confidence-level upper limits on the branching fractions between $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ and $44\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ depending on the channel. In most cases, these results represent either the first limits or significant improvements on existing limits for the decay modes studied.