Extraction of the [formula omitted] coupling from [formula omitted] decays

Abstract

The decays D ∗ → Dπ and D ∗ → Dγ are well described by heavy meson chiral perturbation theory. With the recent measurement of B (D ∗+ → D +γ), the D ∗0, D ∗+ and D s ∗ branching fractions can be used to extract the D ∗Dπ and D ∗Dγ couplings g and β. The D ∗ → Dγ decays receive important corrections at order √ m q and, from the heavy quark magnetic moment, at order 1/ m c . Here all the decay rates are computed to one loop, to first order in m q and 1/ m c , including the effect of heavy meson mass splittings, and the counterterms at order m q . A fit to the experimental data gives two possible solutions, g = 0.27 −0.02−0.02 +0.04+0.05, β= 0.85 −0.1 − 0.1 +0.2 + 0.3 GeV − or g = 0.76 −0.03 −0.1 +0.03+0.2, β = 4.90 −0.3−0.7 +0.3+5.0 GeV −1. The first errors are experimental, while the second are estimates of the uncertainty induced by the counterterms. (The experimental limit Γ D ∗+ < 0.13 MeV excludes the g = 0.76 solution.) Predictions for the D ∗ and B ∗ widths are given.