Search forB+→ℓ+νℓγdecays with hadronic tagging using the full Belle data sample
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Abstract
We search for the decay ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\ell}}^{+}{\ensuremath{\nu}}_{\ensuremath{\ell}}\ensuremath{\gamma}$ with ${\ensuremath{\ell}}^{+}={e}^{+}$ or ${\ensuremath{\mu}}^{+}$ using the full Belle data set of $772\ifmmode\times\else\texttimes\fi{}{10}^{6}B\overline{B}$ pairs, collected at the $\mathrm{\ensuremath{\Upsilon}}(4\mathrm{S})$ resonance with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider. We reconstruct one $B$ meson in a hadronic decay mode and search for the ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\ell}}^{+}{\ensuremath{\nu}}_{\ensuremath{\ell}}\ensuremath{\gamma}$ decay in the remainder of the event. We observe no significant signal within the phase space of ${E}_{\ensuremath{\gamma}}^{\text{sig}}>1\text{ }\text{ }\mathrm{GeV}$ and obtain upper limits of $\mathcal{B}({B}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\nu}}_{e}\ensuremath{\gamma})<6.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$, $\mathcal{B}({B}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\gamma})<3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$, and $\mathcal{B}({B}^{+}\ensuremath{\rightarrow}{\ensuremath{\ell}}^{+}{\ensuremath{\nu}}_{\ensuremath{\ell}}\ensuremath{\gamma})<3.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ at 90% credibility level.