Search for long-lived scalar particles in $B^+ \to K^+ \chi (\mu^+\mu^-)$ decays

TL;DR

This paper reports a search for long-lived scalar particles in B+ decays to K+ and dimuons, setting the most stringent limits to date on their production, with no significant excess observed in the data.

Contribution

First search for long-lived scalar particles in B+ decays to K+ and dimuons, providing new upper limits on their branching fractions across a wide mass and lifetime range.

Findings

No significant excess found in the dimuon mass spectrum.

Set upper limits on branching fractions between 2×10^{-10} and 10^{-7}.

Limits are the most stringent to date for this decay channel.

Abstract

A search for a long-lived scalar particle $\chi$ is performed, looking for the decay ${B^+ \to K^+ \chi}$ with ${\chi \to \mu^+\mu^-}$ in $pp$ collision data corresponding to an integrated luminosity of $3\, {\rm fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of $\sqrt{s}=7$ and 8$\,$TeV. This new scalar particle, predicted by Hidden Sector models, is assumed to have a narrow width. The signal would manifest itself as an excess in the dimuon invariant mass distribution over the Standard Model background. No significant excess is observed in the accessible ranges of mass ${250 < m(\chi) < 4700\,\rm MeV/c^2}$ and lifetime ${0.1 < \tau(\chi) < 1000\,\rm ps}$. Upper limits on the branching fraction $\mathcal{B}(B^+ \to K^+ \chi (\mu^+\mu^-))$ at 95% confidence level are set as a function of $m(\chi)$ and $\tau(\chi)$, varying between $2\times10^{-10}$ and $10^{-7}$. These are the most stringent limits to date. The limits are interpreted in the context of a model with a light inflaton particle.