Measurement of D0-D0bar mixing in D0->Ks pi+ pi- decays

We report a measurement of D0-D0bar mixing in D0 -> Ks pi+ pi- decays using a time-dependent Dalitz plot analysis. The results are based on 540 fb-1 of data accumulated by the Belle detector at the KEKB e+e- collider. Assuming negligible CP violation, we measure the mixing parameters $x=(0.80\pm0.29^{+0.09 +0.15}_{-0.07 -0.14})%$ and $y=(0.33\pm0.24^{+0.07 +0.08}_{-0.12 -0.09})%$, where the errors are statistical, experimental systematic, and systematic due to the Dalitz decay model, respectively.