Lattice QCD simulation of the Z + c channel Sasa

We discuss the lattice QCD simulations that search for the Z+ c with the unconventional quark content c̄cd̄u in the channel IG(JPC) = 1+(1+−). The major challenge is presented by the two-meson states J/ψ π , ψ2Sπ , ψ1Dπ , DD̄∗, D∗D̄∗, ηcρ that are also inevitably present in this channel. The available lattice simulations find expected two-meson eigenstates, but no additional eigenstate as a candidate for Z+ c . This is in a striking contrast to the lattice results in the flavour non-exotic channels, where additional states are found in relation to the most of known resonances and bound states.