High precision measurement of the masses of the $D^0$ and $K_S$ mesons

Using 580 pb$^{-1}$ of $e^+e^-$ annihilation data taken with the CLEO--c detector at $psi(3770)$, the decay $D^0(overline{D}^0)to K^pmpi^mp pi^+pi^-$ has been studied to make the highest precision measurement of $D^0$ mass, $M(D^0)=1864.845pm0.025pm0.022pm0.053$ MeV, where the first error is statistical, the second error is systematic, and the third error is due to uncertainty in kaon masses. As an intermediate step of the present investigation the mass of the $K_S$ meson has been measured to be $M(K_S)=497.607pm0.007pm0.015$ MeV. Both $M(D^0)$ and $M(K_S)$ are the most precise single measurements of the masses of these mesons.