Measurement of the ratio of branching fractions B(B{sup {+-}}{yields}J/{psi}{pi}{sup {+-}})/B(B{sup {+-}}{yields}J/{psi}K{sup {+-}})

We report a measurement of the ratio of branching fractions of the decays B{sup {+-}}{yields}J/{psi}{pi}{sup {+-}} and B{sup {+-}}{yields}J/{psi}K{sup {+-}} using the CDF II detector at the Fermilab Tevatron Collider. The signal from the Cabbibo-suppressed B{sup {+-}}{yields}J/{psi}{pi}{sup {+-}} decay is separated from B{sup {+-}}{yields}J/{psi}K{sup {+-}} using the B{sup {+-}}{yields}J/{psi}K{sup {+-}} invariant mass distribution and the kinematical differences of the hadron track in the two decay modes. From a sample of 220 pb{sup -1} of pp collisions at {radical}(s)=1.96 TeV, we observe 91{+-}15 B{sup {+-}}{yields}J/{psi}{pi}{sup {+-}} events together with 1883{+-}34 B{sup {+-}}{yields}J/{psi}K{sup {+-}} events. The ratio of branching fractions is found to be B(B{sup {+-}}{yields}J/{psi}{pi}{sup {+-}})/B(B{sup {+-}}{yields}J/{psi}K{sup {+-}})=(4.86{+-}0.82(stat){+-}0.15(syst))%.