Measurement of the ratio of branching fractions B(D0 ---> K+ pi-) / B(D0 ---> K- pi+) using the CDF II Detector

The authors present a measurement of R{sub B}, the ratio of the branching fraction for the rare decay D{sup 0} {yields} K{sup +}{pi}{sup -} to that for the Cabibbo-favored decay D{sup 0} {yields} K{sup -}{pi}{sup +}. Charge conjugate decays are implicitly included. A signal of 2005 {+-} 104 events for the decay D{sup 0} {yields} K{sup +}{pi}{sup -} is obtained using the CDF II detector at the Fermilab Tevatron collider. The data set corresponds to an integrated luminosity of 0.35 fb{sup -1} produced in {bar p}p collisions at {radical}s = 1.96 TeV. Assuming no mixing, they find R{sub B} = [4.05 {+-} 0.21(stat) {+-} 0.11(syst)] x 10{sup -3}. This measurement is consistent with the world average, and comparable in accuracy with the best measurements from other experiments.