The nature of near-threshold XYZ states

Abstract

We demonstrate that the recently observed $X$, $Y$, $Z$ states cannot be purely from kinematic effect. Especially the narrow near-threshold structures in elastic channels call for nearby poles of the $S$-matrix which are qualified as states. We propose a way to distinguish cusp effects from genuine states and demonstrate that (not all of) the recently observed $X$, $Y$, $Z$ states cannot be purely from kinematic effects. Especially, we show that the narrow near-threshold structures in elastic channels call for nearby poles of the $S$-matrix, since the normal kinematic cusp effect cannot produce that narrow structures in the elastic channels in contrast to genuine $S$-matrix poles. In addition, it is also discussed how spectra can be used to distinguish different scenarios proposed for the structure of those poles, such as hadro-quarkonia, tetraquarks and hadronic molecules. The basic tool employed is heavy quark spin symmetry.

8 pages, 5 figures, proceeding of NSTAR2015, Osaka, Japan

References in corpus (20)

• 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
• Production of the X(3872) in charmonia radiative decays
• X(3872) as a hadronic molecule and its decays to charmonium states and pions
• Could the near-threshold $XYZ$ states be simply kinematic effects?
• Implications of heavy quark spin symmetry on heavy meson hadronic molecules
• Employing spin symmetry to disentangle different models for the XYZ states
• Y(4260) and Y(4360) as mixed hadrocharmonium
• Y(4260): hadronic molecule versus hadro-charmonium interpretation
• Chromomagnetism, flavour symmetry breaking and S-wave tetraquarks
• $Z_c(4025)$ as the hadronic molecule with hidden charm
• Line shapes in Υ(5S) \to B^{(*)} \bar{B}^{(*)}πwith Z(10610) and Z(10650) using effective field theory
• Resolving the puzzling decay patterns of charged $Z_c$ and $Z_b$ states
• Isovector and hidden-beauty partners of the X(3872)