Extraction of the D^*D\pi coupling from D^* decays

The decays D^* -> D\pi and D^* -> D\gamma are well described by heavy meson chiral perturbation theory. With the recent measurement of Br(D^{+} -> D^+ \gamma), the D^{0}, D^{+}, and D_s^ branching fractions can be used to extract the D^D\pi and D^D\gamma couplings $g$ and $\beta$. The D^ -> D\gamma decays receive important corrections at order $\sqrt{m_q}$ and, from the heavy quark magnetic moment, at order $1\mathrm{/}{m}_c$. Here all the decay rates are computed to one-loop, to first order in $m_q$ and $1\mathrm{/}{m}_c$, 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^{+.04}{-.02}^{+.05}{-.02}, \beta=0.85^{+.2}{-.1}^{+.3}{-.1} GeV^{-1} or g=0.76^{+.03}{-.03}^{+.2}{-.1}, \beta=4.90^{+.3}{-.3}^{+5.0}{-.7} GeV^{-1}. The first errors are experimental, while the second are estimates of the uncertainty induced by the counterterms. (The experimental limit \Gamma_{D^{+}} < 0.13 MeV excludes the $g=0.76$ solution.) Predictions for the D^* and B^* widths are given.