A search is presented for hidden-sector bosons, $\chi$, produced in the decay $B^0\to K^{*}(892{)}^0\chi$, with $K^{*}(892{)}^0\to K^{+}{\pi }^{-}$ and $\chi \to {\mu }^{+}{\mu }^{-}$. The search is performed using $pp$-collision data corresponding to $3.0{\mathrm{fb}}^{-1}$ collected with the LHCb detector. No significant signal is observed in the accessible mass range $214\le m(\chi )\le 4350\mathrm{MeV}$, and upper limits are placed on the branching fraction product $\mathcal{B}\mathbf{(}{B}^0\to K^{*}(892{)}^0\chi \mathbf{)}\times \mathcal{B}(\chi \to {\mu }^{+}{\mu }^{-})$ as a function of the mass and lifetime of the $\chi$ boson. These limits are of the order of $10^{-9}$ for $\chi$ lifetimes less than 100 ps over most of the $m(\chi )$ range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.

• Received 18 August 2015

DOI:https://doi.org/10.1103/PhysRevLett.115.161802

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© 2015 CERN, for the LHCb Collaboration