Searches for $B^0\to K^+\pi^-\tau^+\tau^-$ and $B_s^0\to K^+K^-\tau^+\tau^-$ decays

Abstract

The first searches for $B^0\to K^+\pi^-\tau^+\tau^-$ and $B^0_s\to K^+K^-\tau^+\tau^-$ decays at the LHCb experiment are conducted with $pp$ collision data corresponding to an integrated luminosity of $5.4\textrm{ fb}^{-1}$. The tau leptons are reconstructed using the $\tau^+\to \mu^+\overline{\nu}_\tau\nu_\mu$ decay and the results are presented in bins of $K^+\pi^-$ or $K^+K^-$ mass. No signal is observed and upper limits are set on the branching fractions. The searches result in the first upper limits for $B^0\to K^+\pi^-\tau^+\tau^-$ decays outside the $K^*(892)^0$ region in $K^+\pi^-$ mass and the first limits for $B^0_s\to K^+K^-\tau^+\tau^-$ decays. The searches are recast into limits on the decays $B^0\to K^*(892)^0\tau^+\tau^-$ and $B^0_s\to \phi(1020)\tau^+\tau^-$, yielding $2.8\times10^{-4}$ ($2.5\times10^{-4}$) and $4.7\times10^{-4}$ ($4.1\times10^{-4}$) at the $95\%$ ($90\%$) confidence level, respectively. For the decay $B^0\to K^*(892)^0\tau^+\tau^-$, this result improves on the current best upper limit by an order of magnitude.