S. X. Nakamura, K. Tsushima

Physical Review D , Volume 100 (2019)

09/09/2019

Abstract

Zc(4430) discovered by the Belle Collaboration and confirmed by the LHCb Collaboration in B¯¯¯0→ψ(2S)K−π+ is generally considered to be a charged charmoniumlike state that includes minimally two quarks and two antiquarks. Zc(4200) found in B¯¯¯0→J/ψK−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 Zc(4430) and Zc(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 Zc(4430) and Zc(4200) from the experimental analyses. Applying this idea to Λ0b→J/ψpπ−, we also identify triangle singularities that behave like Zc(4200), but no triangle diagram is available for Zc(4430). This is consistent with LHCb’s finding that their description of the Λ0b→J/ψpπ− data is significantly improved by including a Zc(4200) contribution while Zc(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.

10.1103/PhysRevD.100.051502