  We investigate the decay $B_s^0 \rightarrow J/\psi K^+ K^-$ for invariant
masses of the $K^+K^-$ pair in the range $1.35<M(K^+K^-)<2$ GeV. The data
sample corresponds to an integrated luminosity of 10.4 fb$^{-1}$ of $p \bar{p}$
collisions at $\sqrt{s} = 1.96$ TeV accumulated with the D0 detector at the
Fermilab Tevatron collider. From the study of the invariant mass and spin of
the $K^+K^-$ system, we find evidence for the two-body decay \bsf and measure
the relative branching fraction of the decays \bsf and \bsdec to be
$R_{f_2^{\prime}/\phi} = 0.19 \pm 0.05 \rm \thinspace{(stat)} \pm 0.04 \rm
\thinspace{(syst)}$.
