Search for D0--anti-D0 mixing in the decays D0 --> K+ pi- pi+ pi-
  We present a search for D0--anti-D0 mixing in the decays D0 --> K+ pi- pi+ pi- using 230.4 fb-1 of data collected with the BaBar detector at the PEP-II e+ e- collider at SLAC. Assuming CP conservation, we measure the time-integrated mixing rate R_M = (0.019 +0.016/-0.015(stat.) +/- 0.002(syst.))%, and R_M < 0.048% at the 95% confidence level. Using a frequentist method, we estimate that the data are consistent with no mixing at the 4.3% confidence level. We present results both with and without the assumption of CP conservation. By combining the value of R_M from this analysis with that obtained from an analysis of the decays D0 --> K+ pi- pi0, we find R_M = (0.020 +0.011/-0.010)%, where the uncertainty is statistical only. We determine the upper limit R_M < 0.042% at the 95% confidence level, and we find the combined data are consistent with the no-mixing hypothesis at the 2.1% confidence level. 
The BABAR Collaboration, B. Aubert, et al