Extraction of the D*Dπ coupling from D* 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.