PRD 87, 11( 2013) 112012

Parameter	Measurement
\(\frac {{\cal{B}} (B_c^{-} \to J/\psi D_s^{-})} {{\cal{B}} (B_c^{-} \to J/\psi \pi^{-})}\)	\([2.90 \pm 0.57\mbox{ (stat)} \pm 0.24\mbox{ (syst)}]\)