Evidence for D^{0}-D[over ¯]^{0} Mixing

We present evidence for D0-D̅ 0 mixing in D0→K+π- decays from 384  fb-1 of e+e- colliding-beam data recorded near √s=10.6  GeV with the BABAR detector at the PEP-II storage rings at the Stanford Linear Accelerator Center. We find the mixing parameters x′2=[-0.22±0.30(stat)±0.21(syst)]×10-3 and y′=[9.7±4.4(stat)±3.1(syst)]×10-3 and a correlation between them of -0.95. This result is inconsistent with the no-mixing hypothesis with a significance of 3.9 standard deviations. We measure RD, the ratio of doubly Cabibbo-suppressed to Cabibbo-favored decay rates, to be [0.303±0.016(stat)±0.010(syst)]%. We find no evidence for CP violation.