
\subsection*{Charm Physics}
\vskip-8pt
The influence of New Physics on the charm sector is often
overlooked. Constraints on flavor-changing neutral currents from new physics
in the up quark sector are much weaker than in the down quark sector. Thus high sensitivity studies of rare charm decays offer the possibility of isolating New Physics effects in $\DzDzb$ mixing, in \CP violation and in rare decay branching fractions.

The recent observation of substantial $\DzDzb$ mixing raises the very exciting possibility of measuring \CP violation in charm decays. Many of the most sensitive measurements remain statistics limited even with \superb\-size data samples, providing a substantial motivation for gathering a sample many times that possible with the KEKB upgrade.

In several specific cases, \CP violation in mixing can be studied more precisely by taking advantage of the clean environment provided by exclusive $\DzDzb$ production at the $\psi(3770)$ resonance.  We have therefore included in the \superb\ design the unique capability of running at this center-of mass-energy. Long data-taking runs are not required; a run of two months duration at the $\psi(3770)$ would yield a data sample an order of magnitude larger than the total BES-III sample at that energy.


