Measurement of D0-D0bar mixing using the ratio of lifetimes for the decays D0 -> K- pi+, K- K+, and pi- pi+

We present a measurement of $D^0$-$\bar{D^0}$ mixing parameters using the ratios of lifetimes extracted from a sample of $D^0$ mesons produced through the process $D^{*+}\to\D^0\pi^+$, that decay to $K^{+}\pi^{-}$, K^{-}K^{+}$, or $\pi^-\pi^+$. The Cabibbo-suppressed modes $K^{-}K^{+}$ and $\pi^-\pi^+$ are compared to the Cabibbo-favored mode $K^{+}\pi^{-}$ to obtain a measurement of $y_{CP}$, which in the limit of CP conservation corresponds to the mixing parameter $y$. The analysis is based on a data sample of 384 $fb^{-1}$ collected by the $BaBar$ detector at the PEP-II asymmetric-energy $e^+e^-$ collider. We obtain $y_{CP} = [1.24\pm 0.39\mathrm{(stat)} \pm 0.13\mathrm{(syst)}]%$, which is evidence of $D^0$-$\bar{D^0}$ mixing at the $3\sigma$ level, and $\Delta Y = [-0.26\pm 0.36\mathrm{(stat)} \pm 0.08 \mathrm{(syst)}]%$, where $\Delta Y$ constrains possible CP violation. Combining this result with a previous $BaBar$ measurement of $y_{CP}$ obtained from a separate sample of $D^0\to K^{-}K^{+}$ events, we obtain $y_{CP} = [1.03\pm 0.33 \mathrm{(stat)} \pm 0.19 \mathrm{(syst)}]%$.