Could the near-threshold $XYZ$ states be simply kinematic effects?

Abstract

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 to 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.

Accepted by Phys. Rev. D as a rapid communication

References in corpus (13)

• Heavy quarkonium: progress, puzzles, and opportunities
• Charmonium
• The Z(4430) and a New Paradigm for Spin Interactions in Tetraquarks
• Hadro-Charmonium
• Pion Interactions in the X(3872)
• The Heavy Quark Spin Symmetry Partners of the X(3872)
• Are Y(4260) and {\rm Z${}_2^{+}$(4250)} ${\mathrm{D}}_1\mathrm{D}$ or ${\mathrm{D}}_0{\mathrm{D}}^{\ast }$ Hadronic Molecules?
• Is X(3872) a molecule?
• Isospin breaking effects in the X(3872) resonance
• $Z_b$ and $Z_c$ Exotic States as Coupled Channel Cusps
• X(3872) as a hadronic molecule and its decays to charmonium states and pions
• Exotic Heavy Quarkonium Spectroscopy: A Mini-review
• Resolving the puzzling decay patterns of charged $Z_c$ and $Z_b$ states

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