Search for hidden-sector bosons in $B^0 \!\to K^{*0}\mu^+\mu^-$ decays

TL;DR

This paper reports a search for hidden-sector bosons in B0 decays using LHCb data, setting new upper limits on their production and decay, with no significant signals observed.

Contribution

It provides the most stringent constraints to date on low-mass bosons in B0 decays, using a comprehensive search over a wide mass and lifetime range.

Findings

No significant signal observed for hidden-sector bosons.

Upper limits on branching fractions are around 10^{-9}.

Constraints are placed on theories predicting low-mass bosons.

Abstract

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 fb$^{-1}$ collected with the LHCb detector. No significant signal is observed in the accessible mass range $214 \leq m({\chi}) \leq 4350$ MeV, and upper limits are placed on the branching fraction product $\mathcal{B}(B^0\!\to K^*(892)^0\chi)\times\mathcal{B}(\chi\!\to\mu^+\mu^-)$ 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.