Absolute Hadronic $D$ Branching Ratios and $\psi(3770)$ to $D\overline D$ Cross Sections

We report on a measurement of the branching fractions of three all-hadronic decay modes of the $D^0$ and six of the $D^+$, including the modes $D^0 \rightarrow K^-\pi^+$ and $D^+ \rightarrow K^-\pi^+\pi^+$, using 60 pb$^{-1}$ of data from the CLEO-c detector. We exploit the pair production of D mesons in decays of the $\psi(3770)$ resonance to obtain the branching fractions without reference to the luminosity of the sample. When combined with the luminosity, we obtain a measurement of the production cross-section of $D \overline{D}$ pairs in $e^+ e^-$ collisions at 3.77 GeV center of mass energy.