Search for D0-D̄0 mixing using doubly flavor tagged semileptonic decay modes

We have searched for D0-D̄0 mixing in D*+→π+D0 decays with D0→K(*)eν in a sample of e+e-→cc̄ events produced near 10.58 GeV. The charge of the slow pion from charged D* decay tags the charm flavor at production, and it is required to be consistent with the flavor of a fully reconstructed second charm decay in the same event. We observe 3 mixed candidates compared to 2.85 background events expected from simulation. We ascribe a 50% systematic uncertainty to this expected background rate. We find a central value for the mixing rate of 0.4×10-4. Using a frequentist method, we set corresponding 68% and 90% confidence intervals at (-5.6,7.4)×10-4 and (-13,12)×10-4, respectively.