We study the $e^+ e^- \to K^+ ( D_s^{ *-} D^0 + D_s^- D^{ *0})$ reaction recently measured at BESIII, from where a new $Z_{ cs}$ state has been reported. We study the interaction of $\bar D_s D^*$ with the coupled channels $J/\psi K^-$, $K^{ *-} \eta_c$, $D_s^- D^{ *0}$, $D_s^{ *-} D^0$ by means of an extension to the charm sector of the local hidden gauge approach. We find that the $D_s^- D^{ *0}+ D_s^{ *-} D^0$ combination couples to $J/\psi K^-$ and $K^{ *-} \eta_c$, but the $D_s^- D^{ *0}- D_s^{ *-} D^0$ combination does not. The coupled channels help to build up strength in the $D_s^- D^{ *0}+ D_s^{ *-} D^0$ diagonal scattering matrix close to threshold and, although the interaction is not strong enough to produce a bound state or resonance, it is sufficient to produce a large accumulation of strength at the $\bar D_s D^*$ threshold in the $e^+ e^- \to K^+ ( D_s^{ *-} D^0 + D_s^- D^{ *0})$ reaction in agreement with experiment.
Categories: hep-ph hep-ex