The Charm Physics Potential of a Tau - Charm Factory ∗ †

The charm physics program accessible to a Tau-Charm Factory is summarized. Semileptonic, leptonic, hadronic, rare and forbidden charm decay modes are discussed, as well as D 0 − ¯ D 0 mixing and CP violation in the charm sector. The theoretical expectations in the Standard Model and beyond as well as the experimental capabilities of a Tau-Charm Factory are examined for each of the above processes. One of the outstanding problems in particle physics is the origin of the fermion mass and mixing spectrum. At present the best approach in addressing this question is to study the properties of all heavy fermions in detail. While investigations of the K and B systems have and will continue to play a central role in the quest to understand flavor physics, in-depth examinations of the charm-quark sector have yet to be performed , leaving a gap in our knowledge. Since charm is the only heavy charged +2/3 quark presently accessible to experiment, it provides the sole window of opportunity to examine flavor physics in this sector. In addition, charm allows a complimentary probe of Standard Model (SM) physics (and beyond) to that attainable from the down-quark sector. Detailed measurements of heavy quark systems are best realized at high precision, high luminosity machines. Here we discuss the charm physics potential at a high lumi-nosity (L = 10 33 cm −2 sec −1) e + e − collider operating at the c¯ c and τ ¯ τ threshold region, i.e., a Tau-Charm Factory (τ cF). Such a machine would facilitate an in-depth analysis of the charm-quark sector (as well as τ-lepton 1 and charmonium 2 studies) without the contamination of b-quark production. The high luminosity is absolutely essential in order to accomplish the physics goals of the machine. In some cases it is necessary in order to measure a reaction at the high level of precision that is desired, while in other cases, high luminosity is required to reach the very small transition rates.