Search for Exclusive B Decays to J and $\eta$ or $\pi^{0}$ with the L3 Detector

A search for exclusive decays of $\ensuremath{\mathrm{B_d^0}}$ and $\ensuremath{\mathrm{B_s^0}}$ mesons has been performed in the channels $\ensuremath{\mathrm{B_d^0}\rightarrow\mathrm{J}\eta}$,\,\, $\ensuremath{\mathrm{B_s^0}\rightarrow\mathrm{J}\eta}$,\,\, $\ensuremath{\mathrm{B_d^0}\rightarrow\mathrm{J}\pi^0}$ and $\ensuremath{\mathrm{B_s^0}\rightarrow\mathrm{J}\pi^0}$. The data sample consisted of more than three and half million hadronic $\ensuremath{\mathrm {Z}}$ decays collected by the L3 experiment at LEP from 1991 through 1995. No candidate events have been observed for any of the modes thus determining upper limits at 90\% confidence level: $3.2\times 10^{-4}$ on $\mathrm{Br}(\ensuremath{\mathrm{B_d^0}\ rightarrow\mathrm{J}\pi^0)}$ and the first experimental limits: \begin{eqnarray*} \mathrm{Br}(\ensuremath{\mathrm{B_d^0}\rightarrow \mathrm{J}\eta}) & < & 1.2\times 10^{-3},\\ \mathrm{Br}(\ensuremath{\m athrm{B_s^0}\rightarrow\mathrm{J}\eta}) & < & 3.8\times 10^{-3},\\ \mathrm{Br}(\ensuremath{\mathrm{B_s^0}\rightarrow\mathrm {J}\pi^0}) & < & 1.2\times 10^{-3}.\\ \end{eqnarray*}