Charmoniumlike Channels 1^+ with Isospin 1 from Lattice and Effective Field Theory

Many exotic charmoniumlike mesons have already been discovered experimentally, of which the Z_c mesons with isospin 1 are prominent examples. We investigate J^PC=1^+± states with flavor c̅c q̅q (q=u,d) in isospin 1 using lattice QCD. This is the first study of these mesons employing more than one volume and involving frames with nonzero total momentum. We utilize two N_f=2+1 CLS ensembles with m_π≃ 280MeV. As the simulations are performed with unphysical quark masses and at a single lattice spacing of a=0.086fm, our results provide only qualitative insights. Resulting eigenenergies are compatible or just slightly shifted down with respect to noninteracting energies, where the most significant shifts occur for certain DD̅^* states. Both channels 1^+± have a virtual pole slightly below the threshold if DD̅^* is assumed to be decoupled from other channels. In addition, we perform a coupled channel analysis of J/ψπ and DD̅^* scattering with J^PC=1^+- within an effective field theory framework. The J/ψπ and DD̅^* invariant-mass distributions from BESIII and finite-volume energies from several lattice QCD simulations, including this work, are fitted simultaneously. All fits yield two poles relatively close to the DD̅^* threshold and reasonably reproduce the experimental Z_c peaks. They also reproduce lattice energies up to slightly above the DD̅^* threshold, while reproduction at even higher energies is better for fits that put more weight on the lattice data. Our findings suggest that the employed effective field theory can reasonably reconcile the peaks in the experimental line shapes and the lattice energies, although those lie close to noninteracting energies. We also study J/ψπ scattering in s-wave and place upper bounds on the phase shift.