Configuration mixing in strange tetraquarks Zcs

The BESIII Collaboration has observed a candidate for a cc¯sū tetraquark Zcs at (3982.5-2.6+1.8±2.1) MeV and width (12.8-4.4+5.3±3.0) MeV, while the LHCb Collaboration has observed a Zcs candidate in the J/ψK- channel with mass of (4003±6-14+4) MeV and width (131±15±26) MeV. In this paper, we examine the possibility that these two states are distinct eigenstates of a mixing process similar to that which gives rise to two axial-vector mesons labeled by the Particle Data Group [P. Zyla et al., Prog. Theor. Exp. Phys. 6, 083C01 (2020)PTEPCR2050-3911] K1(1270) and K1(1400). The main point is that on top of a c¯c pair the Zcs states have the same light quark content as the K1-s. In the compact tetraquark picture, this implies several additional states, analogous to members of the K1 nonet. These states have not yet been observed; nor are they required in the molecular approach. Thus, experimental discovery or exclusion of these extra states will be a critical test for competing models of exotic mesons with hidden charm.