Study ofBDecays to Charmonium States:B→ηcKandB→χc0K

In a sample of $9.66\times {10}^{6}B\overline{B}$ pairs collected with the CLEO detector we make the first observation of $B$ decays to an ${\eta }_c$ and a kaon. We measure branching fractions $B(B^{+}\to {\eta }_c{K}^{+})=({0.69}_{-0.21\mathrm{}}^{+0.26\mathrm{}}\pm 0.08\pm 0.20)\times {10}^{-3\mathrm{}}$ and $B(B°\to {\eta }_{c}K°)=({1.09}_{-0.42\mathrm{}}^{+0.55\mathrm{}}\pm 0.12\pm 0.31)\times {10}^{-3\mathrm{}}$, where the first error is statistical, the second is systematic, and the third is from the ${\eta }_c$ branching fraction uncertainty. From these we extract the ${\eta }_c$ decay constant in the factorization approximation, $f_{{\eta }_c}=335\mathrm{}\pm 75\mathrm{MeV}$. We also search for $B$ decays to a ${\chi }_{c0\mathrm{}}$ and a kaon. No evidence for a signal is found and we set $90\%$ C.L. upper limits: $B(B^{+}\to {\chi }_{c0\mathrm{}}{K}^{+})<4.8\mathrm{}\times {10}^{-4\mathrm{}}$ and $B(B°\to {\chi }_{c0\mathrm{}}K°)<5.0\mathrm{}\times {10}^{-4\mathrm{}}$.