Search for the decay B0→K*0τ+τ− at the Belle experiment

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This paper presents a search for the rare flavor-changing neutral current process ${B}^{0}\ensuremath{\rightarrow}{K}^{*0}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ using data taken with the Belle detector at the KEKB asymmetric energy ${e}^{+}{e}^{\ensuremath{-}}$ collider. The analysis is based on the entire $\mathrm{\ensuremath{\Upsilon}}(4S)$ resonance data sample of $711\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, corresponding to $772\ifmmode\times\else\texttimes\fi{}{10}^{6}B\overline{B}$ pairs. In our search we fully reconstruct the companion $B$ meson produced in the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Upsilon}}(4S)\ensuremath{\rightarrow}B\overline{B}$ from its hadronic decay modes, and look for the decay ${B}^{0}\ensuremath{\rightarrow}{K}^{*0}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ in the rest of the event. No evidence for a signal is found. We report an upper limit on the branching fraction $\mathcal{B}({B}^{0}\ensuremath{\rightarrow}{K}^{*0}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}})<3.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ at 90% confidence level. This is the first direct limit on $\mathcal{B}({B}^{0}\ensuremath{\rightarrow}{K}^{*0}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}})$.

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