Centro de Física das Interacções Fundamentais

We show that the long known puzzling branching ratios of open-charm decays in e + e − annihilation can be reasonably described with a simple form factor, which strongly suppresses open channels far above threshold. Application to the e + e − → J/ψ ππ data on the X(4260) enhancement recently reported by the BABAR Collaboration [1] allows a good fit with a simple nonresonant cusp structure around the D ∗ sD ∗ s threshold. Moreover, we argue that a closer look at the data reveals an oscillatory pattern, which we model as an interference effect between a fast — OZI-allowed — and a slow — OZI-forbidden — J/ψ f0(980) mode. Other candidates for similar nonresonant enhancements are discussed. Recently, the BABAR Collaboration presented new preliminary data for the reaction e + e − → J/ψ π + π − [1]. These data exhibit a much more pronounced peak in the X(4260) [2] region than in the first BABAR observation of this structure [3], besides a rather constant signal for the remaining invariant masses [4]. The new experimental analysis of the X(4260) using a nonrelativistic Breit-Wigner parametrization yielded a mass of M = ( 4252 ± 6 +2 −3 MeV and a