Leptonic D and D s Decays near cc̄ Threshold

Within the Standard Model, leptonic D (or B) meson decays proceed via annihilation of the initial state quarks. The matrix element is described by the product of a hadronic current, a leptonic current, along with a W propagator. The form of the latter two are well-known within the Standard Model, however, the hadronic matrix element, which represents the annihilation of the initial state heavy quark and light antiquark, depends on the details of the initial-state quark wave-functions, and is not calculable using standard techniques of perturbative QCD. This hadronic matrix element can be computed using either lattice QCD [1, 2, 3], or other techniques [4, 5, 6, 7, 8]. The partial width for the leptonic decay is given by: