The role of charged exotic states in e+e− → ψ(2S) π+π−

Abstract

In this work, we use the dispersion theory to provide a physical description of recent BESIII data on the reaction e+e−→ψ(2S)π+π−. Taking into account explicitly the effects of charged exotic intermediate states in the t- and u-channels as well as the two-pion final state interaction, we describe the invariant mass distribution for four different e+e− center-of-mass energies. The effects of the ππ rescattering are accounted for in a single channel Omnès approach which is found to explain the ππ-invariant mass distributions at all e+e− center-of-mass energies. For q=4.226 GeV and q=4.258 GeV the already established charged exotic state Zc(3900) is considered as the intermediate state, whereas for q=4.358 GeV the rescattering of pions dominates the fits. For the highest energy, q=4.416 GeV, a heavier charged exotic state with mass mZc=4.016(4) GeV and width ΓZc=52(10) MeV is essential to describe the experimental data. Although the mass of this state is consistent with the established Zc(4020), its width is significantly larger.