Measurement of D0-antiD0 mixing parameters using D0 -> K0S pi+ pi- and D0 -> KS0 K+ K- decays

We report a direct measurement of $D^0-overline{D}^0$ mixing parameters through a time-dependent amplitude analysis of the Dalitz plots of $D^0 \rightarrow K_S^0 \pi^+ \pi^-$and,forthefirsttime,$D^0 \rightarrow K_S^0 K^+ K^-$decays\mathrm{.}Thelow-momentumpion$\pi_s^+$inthedecay$D^{*+} \rightarrow D^0 \pi_s^+$identifiestheflavoroftheneutral$D$ meson at its production. Using 468.5 fb${}^{-1}$ of $e^{+}{e}^{-}$ colliding-beam data recorded near $\sqrt{s}=10.6$~GeV by the BABAR detector at the PEP-II asymmetric-energy collider at SLAC, we measure the mixing parameters $x= [1.6 \pm 2.3 ({\rm stat.}) \pm 1.2 ({\rm syst.}) \pm 0.8 ({\rm model}) ] \times10^{-3}$,and$y= [5.7 \pm 2.0 ({\rm stat.}) \pm 1.3 ({\rm syst.}) \pm 0.7 ({\rm model}) ]\times 10^{-3}$\mathrm{.}Theseresultsprovidethebestmeasurementtodateof$x$and$y$. The knowledge of the value of $x$, in particular, is crucial for understanding the origin of mixing.