UC Berkeley

Using 1.3 fb^-1 of data from p-pbar collisions at sqrt{s}=1.96 TeV collected with the CDF II detector at the Fermilab Tevatron, we have measured the relative branching ratio BR(B^- -> D^0 K^-)/BR(B^- -> D^0 pi^-) and its charge conjugate in the D^0 flavor decay mode D^0_f -> K^-pi^+ and the CP-even decay modes D^0 -> K^-K^+ and D^0 -> pi^-pi^+. From these measurements, we derive:

R = (7.99 +- 0.33(stat.) +- 0.38(sys.)) %,

R_{CP+} = 1.15 +- 0.17(stat.) +- 0.02(sys.),

A_{CP+} = 0.10 +- 0.15(stat.) +- 0.02(sys.).

These values are consistent with Standard Model expectations.