Study of B Decays to Charmonium States B→ ηcK and B→ χC₀K

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In a sample of 9.66× 10⁶ BB pairs collected with the CLEO detector we make the first observation of B decays to an ηc and a kaon. We measure branching fractions BR(B+→ηc K+) = (0.69 + 0.26 - 0.21 +- 0.08 +- 0.20)× 10⁻³ and BR(B⁰→ηc K⁰) = (1.09 + 0.55 - 0.42 +- 0.12 +- 0.31)× 10⁻³, where the first error is statistical, the second is systematic and the third is from the ηc branching fraction uncertainty. From these we extract the ηc decay constant in the factorization approximation, fηc = 335 +- 75 MeV. We also search for B decays to a χc₀ and a kaon. No evidence for a signal is found and we set 90% CL upper limits: BR(B+→χc₀ K+) < 4.8× 10⁻⁴ and BR(B⁰→χc₀ K⁰) < 5.0× 10⁻⁴.