Form Factors in D Meson Decays

We study the $d\Gamma / dq^2$ spectra and the branching fractions of the $D$ meson exclusive semileptonic decays with the lepton mass effects into consideration. We investigate their sensitivity to form factor models, and find that the decays to a pseudoscalar meson and a lepton pair are sensitive to the property of the form factor $F_1(q^2)$, and those to a vector meson and a lepton pair to the form factor $A_1(q^2)$. We also analyze the experimental results of the branching fractions $\cal{B} (D^0\to K^- (or \pi^-) \pi^+)$ and $\cal{B} (D^0\to K^- (or \pi^-) e^+ \nu)$, and show that it is implied that $F_1(q^2)$ is of dipole type, instead of simple pole type which is commonly assumed.