Lineshape of ψ(3770) and low-lying vector charmonium resonance parameters in e⁺e^-→DD̅

We investigate the DD̅ 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 ψ^′, though it is below the DD̅ threshold. The recent experimental data from the BES and Belle collaborations allow us to determine the ψ^′DD̅ coupling constant, which appears to be consistent with other theoretical studies. As a consequence, the ψ^′-ψ(3770) mixing parameter can be extracted around the ψ(3770) mass region. Resonance parameters for ψ(3770), X(3900), ψ(4040), and ψ(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 DD̅ ^*+c.c. open channel effects. Our result shows that such a possibility cannot be eliminated.