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Could the near-threshold X Y Z states be simply kinematic effects?

2015; American Physical Society; Volume: 91; Issue: 5 Linguagem: Inglês

10.1103/physrevd.91.051504

1550-7998

Feng-Kun Guo, C. Hanhart, Qian Wang, Q. Zhao,

Particle physics theoretical and experimental studies

We demonstrate that the spectacular structures discovered recently in various experiments and named as $X$, $Y$ and $Z$ states cannot be purely kinematic effects. Their existence necessarily calls for nearby poles in the $S$ matrix and they therefore qualify as states. We propose a way of distinguishing kinematic cusp effects from genuine $S$-matrix poles: the kinematic threshold cusp cannot produce a narrow peak in the invariant mass distribution in the elastic channel in contrast with a genuine $S$-matrix pole.