Observation of D0-(D)over-bar0 Mixing Using the CDF II Detector

We measure the time dependence of the ratio of decay rates for D-0 -> K+ pi(-) to the Cabibbo- favored decay D-0 -> K- pi(+). The charge conjugate decays are included. A signal of 3: 3 x 10(4) D*(+) -> pi D-+(0), D-0 -> K+ pi(-) decays is obtained with D-0 proper decay times between 0.75 and 10 mean D-0 lifetimes. The data were recorded with the CDF II detector at the Fermilab Tevatron and correspond to an integrated luminosity of 9: 6 fb(-1) for p (p) over bar collisions at root s = 1: 96 TeV. Assuming CP conservation, we search for D-0-(D) over bar (0) mixing and measure the mixing parameters to be R-D = (3: 51 +/- 0: 35) x 10(-3), y' = (4: 3 +/- 4: 3) x 10(-3), and x'(2) = (0: 08 +/- 0: 18) x 10(-3). We report Bayesian probability intervals in the x'(2)- y' plane and find that the significance of excluding the no- mixing hypothesis is equivalent to 6.1 Gaussian standard deviations, providing the second observation of D-0-(D) over bar (0) mixing from a single experiment.