Measurement of $\it{D^{0}}$-$\it{\overline{D}{}^{0}}$ Mixing and Search for Indirect $\it{CP}$ Violation Using $\it{{D^0\to K_S^0\pi^+\pi^-}}$ Decays

We report a measurement of ${D}^{0}\text{-}{\overline{D}}^{0}$ mixing parameters and a search for indirect $CP$ violation through a time-dependent amplitude analysis of ${D}^{0}\to {K}_{S}^{0}{\pi }^{+}{\pi }^{-}$ decays. The results are based on $921\text{}\text{}{\mathrm{fb}}^{-1}$ of data accumulated with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{-}$ collider. Assuming $CP$ conservation, we measure the mixing parameters $x=\left(0.56±{0.19}_{-0.09-0.09}^{+0.03+0.06}\right)%$ and $y=\left(0.30±\phantom{\rule{0ex}{0ex}}{0.15}_{-0.05-0.06}^{+0.04+0.03}\right)%$, where the errors are statistical, experimental systematic, and systematic due to the amplitude model, respectively. With $CP$ violation allowed, the parameters $|q/p|={0.90}_{-0.15-0.04-0.05}^{+0.16+0.05+0.06}$ and $\mathrm{arg}\left(q/p\right)=\left(-6±11±{3}_{-4}^{+3}\right)°$ are found to be consistent with conservation of $CP$ symmetry in mixing and in the interference between mixing and decay, respectively.