Lineshape of ψ (3770) and low-lying vector charmonium resonance parameters in e+e- → D(D)over-bar

We investigate the D (D) over bar production in e(+)e(-) annihilations near threshold in an effective Lagrangian approach. This shows that the lineshape of the cross section near threshold is sensitive to the contributions from psi', though it is below the D (D) over bar threshold. The recent experimental data from the BES and Belle collaborations allow us to determine the psi'D (D) over bar coupling constant, which appears to be consistent with other theoretical studies. As a consequence, the psi'-psi(3770) mixing parameter can be extracted around the psi(3770) mass region. Resonance parameters for psi(3770), X(3900), psi(4040), and psi(4160) are also investigated. The X(3900) appears as an enhancement at around 3.9 GeV in the Belle data. In addition to treating it as a resonance, we also study the mechanism through which the enhancement is produced by the D (D) over bar + c.c. open channel effects. Our result shows that such a possibility cannot be eliminated.