  First evidence of the $B^0\to J/\psi\omega$ decay is found and the
$B_{s}^0\to J/\psi\eta$ and $B_{s}^0\to J/\psi\eta^{\prime}$ decays are studied
using a dataset corresponding to an integrated luminosity of 1.0
$\mathrm{fb}^{-1}$ collected by the LHCb experiment in proton-proton collisions
at a centre-of-mass energy of $\sqrt{s} = 7$ TeV. The branching fractions of
these decays are measured relative to that of the $\mathrm{B}^0\to
J/\psi\rho^0$ decay: $$\frac{Br(B^0\to J/\psi\omega)}{Br(B^0\to J/\psi\rho^0)}
= 0.89 \pm0.19(stat)^{+0.07}_{-0.13}(syst)$$ $$\frac{Br(B^0_s\to
J/\psi\eta)}{Br(B^0\to J/\psi\rho^0)} = 14.0 \pm
1.2(stat)^{+1.1}_{-1.5}(syst)^{+1.1}_{-1.0}(\frac{f_d}{f_s}),$$
$$\frac{Br(B^0_s\to J/\psi\eta^{\prime})}{Br(B^0\to J/\psi\rho^0)} =
12.7\pm1.1(stat)^{+0.5}_{-1.3}(syst)^{+1.0}_{-0.9}(\frac{f_d}{f_s}),$$ where
the last uncertainty is due to the knowledge of $f_d/f_s$, the ratio of b-quark
hadronization factors that accounts for the different production rate of $B^0$
and $B^0_s$ mesons. The ratio of the branching fractions of $B^0_s\to
J/\psi\eta^{\prime}$ and $B^0_s\to J/\psi\eta$ decays is measured to be $$
\frac{Br(B^0_s\to J/\psi\eta^{\prime})}{Br(B^0_s\to J/\psi\eta)} =
0.90\pm0.09(stat)^{+0.06}_{-0.02}(syst).$$
