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

Abstract

A search is presented for hidden-sector bosons, $χ$, produced in the decay ${B^0\!\to K^*(892)^0χ}$, with $K^*(892)^0\!\to K^{+}π^{-}$ and $χ\!\toμ^+μ^-$. 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 $214 \leq m(χ) \leq 4350$ MeV, and upper limits are placed on the branching fraction product $\mathcal{B}(B^0\!\to K^*(892)^0χ)\times\mathcal{B}(χ\!\toμ^+μ^-)$ as a function of the mass and lifetime of the $χ$ boson. These limits are of the order of $10^{-9}$ for $χ$ lifetimes less than 100 ps over most of the $m(χ)$ range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.

Figures (8)

• Figure 1: Feynman diagram for the decay $B^0 \!\to K^{*0}\chi$, with $\chi \! \to \mu^+\mu^-$.
• Figure 2: Invariant mass spectrum with fit overlaid for all prompt $B^0 \!\to K^{*0}\mu^+\mu^-$ candidates with $1.1 < m^2(\mu^+\mu^-)\xspace < 6.0\mathrm{\,Ge V}\xspace^2$.
• Figure 3: Distribution of $m(\mu^+\mu^-)$ in the (black) prompt and (red) displaced regions. The shaded bands denote regions where no search is performed due to (possible) resonance contributions. The ${J / \psi }$, $\psi(2S)$ and $\psi(3770)$ peaks are suppressed to better display the search region.
• Figure 4: Upper limits at 95% CL for (left axis) $\mathcal{B}(B^0 \!\to K^{*0}\chi\xspace(\mu^+\mu^-))/\mathcal{B}(B^0 \!\to K^{*0}\mu^+\mu^-\xspace)$, with $B^0 \!\to K^{*0}\mu^+\mu^-$ in $1.1 < m^2(\mu^+\mu^-)\xspace < 6.0\mathrm{\,Ge V}\xspace^2$, and (right axis) $\mathcal{B}(B^0 \!\to K^{*0}\chi\xspace(\mu^+\mu^-))$. The sparseness of the data leads to rapid fluctuations in the limits. Excluding the region near $2m(\mu)$, the relative limits for $\tau < 10\hbox{,ps}\xspace$ are between 0.005--0.05 and all relative limits for $\tau \leq 1000\hbox{,ps}\xspace$ are less than one.
• Figure 5: Exclusion regions at 95% CL: (left) constraints on the axion model of Ref. Freytsis:2009ct; (right) constraints on the inflaton model of Ref. Bezrukov:2014nza. The regions excluded by the theory Bezrukov:2014nza and by the CHARM experiment Bergsma:1985qz are also shown.