Observation of charm mixing at CDF

We report on the observation of D0-D̄0 oscillations by measuring the time-dependent ratio of yields for the rare decay D0 → K+π- to the favored decay D 0→K-π+ at the Collider Detector at Fermilab (CDF). Using 9.6 fb-1of integrated luminosity of√s = 1.96 TeV pp̄ collisions recorded in the full CDF Run II, the signals of 7.6×106 D0 →K-π+ and 33×103 D0 → K+π- decays are reconstructed in D*-tagged events, with proper decay times between 0.75 and 10 mean D0 lifetimes. We measure the mixing parameters x′2= (0.08±0.18)×10-3, y′ = (4.3±4.3)×10-3, and RD = (3.51±0.35)×10-3. Our results are consistent with standard model expectations and similar results from proton-proton collisions and exclude the no-mixing hypothesis with a significance equivalent to 6.1 standard deviations.