Zc(4430 ) and Zc(4200 ) as triangle singularities

Z_c(4430 ) discovered by the Belle Collaboration and confirmed by the LHCb Collaboration in B^¯0→ψ (2 S )K^-π⁺ is generally considered to be a charged charmoniumlike state that includes minimally two quarks and two antiquarks. Z_c(4200 ) found in B^¯0→J /ψ K^-π⁺ by Belle is also a good candidate of a charged charmoniumlike state. In this work, we propose a compelling alternative to the tetraquark-based interpretations of Z_c(4430 ) and Z_c(4200 ). We demonstrate that kinematical singularities in triangle loop diagrams induce a resonancelike behavior that can consistently explain the properties (spin parity, mass, width, and Argand plot) of Z_c(4430 ) and Z_c(4200 ) from the experimental analyses. Applying this idea to Λ_b⁰→J /ψ p π^-, we also identify triangle singularities that behave like Z_c(4200 ), but no triangle diagram is available for Z_c(4430 ). This is consistent with LHCb's finding that their description of the Λ_b⁰→J /ψ p π^- data is significantly improved by including a Z_c(4200 ) contribution while Z_c(4430 ) seems to hardly contribute. Even though the proposed mechanisms have uncertainty in the absolute strengths which are currently difficult to estimate, otherwise the results are essentially determined by the kinematical effects and, thus, robust.