Two-loop Correction to the Leptonic Decay of Quarkonium

Abstract

Applying asymptotic expansions at threshold, we compute the two-loop QCD correction to the short-distance coefficient that governs the leptonic decay $\psi \to l^{+}{l}^{-}$ of a S-wave quarkonium state and discuss its impact on the relation between the quarkonium non-relativistic wave function at the origin and the quarkonium decay constant in full QCD.

Comments: 7 pages, LaTeX, 1 figure included via epsf.sty