Speaker
Description
We analyse the processes $e^+ e^- \to \gamma^* \to J/\psi \pi \pi (K \bar{K})$ and $e^+ e^- \to \gamma^* \to h_c \pi \pi$ using the recently proposed Dalitz-plot decomposition approach, based on the helicity formalism for three-body decays. Within a Lagrangian-based toy model, we validate key aspects of this approach, namely the factorisation of the overall rotation for all decay chains and spin alignments, as well as crossing symmetry between final states. In analysing the experimental data, we describe the subchannel dynamics through a dispersive treatment of $\pi\pi/K\bar{K}$ interactions, reproducing the $f_0(500)$ and $f_0(980)$ pole structures. Using the latest $e^+ e^- \to J/\psi \pi \pi (K \bar{K})$ data in the 4.1271-4.3583 GeV range, we reproduce invariant mass spectra that reveal both $Z_c(3900)$ and $Z_c(4020)$ states and discuss prospects for further constraints on the $Y(4220)$ and $Y(4320)$.
Ermolina, Danilkin, Vanderhaeghen (Phys.Lett.B 864 (2025) 139450)
Ermolina, Danilkin, Vanderhaeghen (in preparation)