Charm physics

Some of the most important charm physics will be the study of semileptonic decays, especially Cabibbo-suppressed decays. Already the decays and are providing important information on the form factors for a heavy quark decaying into a light quark. This serves to improve the picture of the form factors in exclusive decay. Even better would be to make good measurements of the decays and .

At present, the CLEO II sample for , obtained by using , is the largest in the world. The other Cabibbo-favored decays also use the tag technique to remove backgrounds, but in some modes, the background is still fairly large. The ability to separate charm vertices will help somewhat, especially in the case of decay, because of the long lifetime. CLEO has seen a good signal, but the other Cabibbo-suppressed decays are obscured by their Cabibbo-favored counterparts. The decay modes and require good detection of soft 's and charm vertex separation to improve the measurements.

A rare charm decay mode of special importance is the pure leptonic decay , which measures the important decay constant . This decay has been observed in CLEO II but will be measured with much higher precision in the upgraded CLEO experiment using the decay. It will require excellent measurement of the soft photon parameters, and the ability to reject photons from decay. It will also require good reconstruction of the missing neutrino using the technique of hermetic measurement of missing momentum.