Search for the rare decaysB→πℓ+ℓ−andB0→ηℓ+ℓ−

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Abstract

We present the results of a search for the rare flavor-changing neutral-current decays $B\ensuremath{\rightarrow}\ensuremath{\pi}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ ($\ensuremath{\pi}={\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$, ${\ensuremath{\pi}}^{0}$ and $\ensuremath{\ell}=e$, $\ensuremath{\mu}$) and ${B}^{0}\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ using a sample of ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\Upsilon}(4S)\ensuremath{\rightarrow}B\overline{B}$ decays corresponding to $428\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity collected by the BABAR detector. No significant signal is observed, and we set an upper limit on the isospin and lepton-flavor averaged branching fraction of $\mathcal{B}(\mathcal{B}\ensuremath{\rightarrow}\ensuremath{\pi}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}})<5.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ and a lepton-flavor averaged upper limit of $\mathcal{B}({\mathcal{B}}^{0}\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}})<6.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$, both at the 90% confidence level. We also report 90% confidence level branching fraction upper limits for the individual modes ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{e}^{+}{e}^{\ensuremath{-}}$, ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{e}^{+}{e}^{\ensuremath{-}}$, ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, ${B}^{0}\ensuremath{\rightarrow}\ensuremath{\eta}{e}^{+}{e}^{\ensuremath{-}}$, and ${B}^{0}\ensuremath{\rightarrow}\ensuremath{\eta}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$.

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