Study of B±→J/ψπ± and B±→J/ψK± decays: Measurement of the ratio of branching fractions and search for direct CP-violating charge asymmetries

We have studied the B±→J/ψπ± and B±→J/ψK± decays using a 20.7 fb-1 data set collected with the BABAR detector. We observe a signal of 51±10 B±→J/ψπ± events and determine the ratio B(B± →J/ψπ±)/B(B±→J/ψ K±) to be [3.91±0.78(stat)±0.19(syst)]%. The CP-violating charge asymmetries for the B±→J/ψπ± and B±→J/ψK± decays are determined to be Aπ=0.01±0.22(stat)±0.01(syst) and AK =0.003±0.030(stat)±0.004(syst).