Are the XYZ states unconventional states or conventional states with unconventional properties?

Abstract

We discuss three possible scenarios for the interpretation of mesons containing a heavy quark and its antiquark near and above the first threshold for a decay into a pair of heavy mesons in a relative $S$--wave. View I assumes that these thresholds force the quark potential to flatten which implies that while in these energy ranges molecular states may be formed there should not be any quark--anti-quark states above these thresholds. View II assumes that the main part of the interaction between two mesons is due to the poles which originate from the $Q\bar{Q}$ interaction. The properties of the $Q\bar{Q}$ mesons are strongly influenced by opening thresholds but the number of states is given by the quark model. In View III, both types of mesons are admitted also near and above the open flavor thresholds: $Q\bar{Q}$ mesons and dynamically generated mesons. Experimental consequences of these different views are discussed.

arXiv comment15 pages, 5 figures

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• The $XYZ$ states: experimental and theoretical status and perspectives
• Scalar mesons and the fragmented glueball
• Prediction of a narrow exotic hadronic state with quantum numbers $J^{PC}=0^{--}$
• Is $Z_{cs}(3982)$ a molecular partner of $Z_c(3900)$ and $Z_c(4020)$ states?
• $P$-wave charmonium contribution to hidden-charm states from reanalysis of lattice QCD data
• Bottomonium spectroscopy in the quark-gluon plasma
• Production of $1^{-+}$ exotic charmonium-like states in electron-positron collisions
• Hints of the $J^{PC}=0^{--}$ and $1^{--}$ $K^{\ast }{\bar{K}}_1(1270)$ Molecules in the $J/\psi \to \varphi \eta {\eta }^{\prime }$ Decay