QCD Exotics

Abstract

QCD-motivated models for hadrons predict an assortment of "exotic" hadrons that have structures that are more complex then the quark-antiquark mesons and three-quark baryons of the original quark-parton model. These include pentaquark baryons, the six-quark H-dibaryon, and tetra-quark, hybrid, and glueball mesons. Despite extensive experimental searches, no unambiguous candidates for any of these exotic configurations have yet to be identified. On the other hand, a number of meson states, one that seems to be a proton-antiproton bound state, and others that contain either charmed-anticharmed quark pairs or bottom-antibottom quark pairs, have been recently discovered that neither fit into the quark-antiquark meson picture nor match the expected properties of the QCD-inspired exotics. Here I briefly review results from a recent search for the H-dibaryon, and discuss some properties of the newly discovered states --the so-called XYZ mesons-- and compare them with expectations for conventional quark-antiquark mesons and the predicted QCD-exotic states.

11 pages, 8 figures, to appear in the proceedings of LEAP 2013

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• Observation of a charged charmoniumlike structure Z_c(4020) and search for the Z_c(3900) in e+e- to pi+pi-h_c
• Determination of the X(3872) meson quantum numbers
• Observation of a near-threshold omega-J/psi mass enhancement in exclusive B-->K omega J/psi decays
• Observation of a charged (DD*bar)- mass peak in e+e- --> pi+ (DD*bar)- at Ecm=4.26 GeV
• Observation of a near-threshold enhancement in th p pbar mass spectrum from radiative J/psi-->gamma p pbar decays
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• Observation of two resonance-like structures in the pi+ chi_c1 mass distribution in exclusive B0-bar --> K- pi+ chi_c1 decays
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• Observation of Y(3940) -> J/psi omega in B -> J/psi omega K at BABAR
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• First observation of the P-wave spin-singlet bottomonium states h_b(1P) and h_b(2P)
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• Observation of a charmonium-like enhancement in the gamma gamma --> omega J/psi process
• Study of X(3915) --> J/ψω in two-photon collisions
• Spin-Parity Analysis of ppbar Mass Threshold Structure in J/psi and psi' Radiative Decays
• Observation of B+ -> p pbar pi+, B0 -> p pbar K0, and B+ -> p pbar K*+
• Observation of an enhancement in e+e- to Upsilon(1S)pi+pi-, Upsilon(2S)pi+pi-, and Upsilon(3S)pi+pi- production near sqrt{s}=10.89 GeV at Belle
• Observation of an enhancement in $e^{+}{e}^{-}\to {\rm Y}(1S){\pi }^{+}{\pi }^{-}$, ${\rm Y}(2S){\pi }^{+}{\pi }^{-}$, and ${\rm Y}(3S){\pi }^{+}{\pi }^{-}$ production around $\sqrt{s}=10.89$ GeV at Belle
• Proton-Antiproton Annihilation in Baryonium
• Radiative Decays of the Upsilon(1S) to a Pair of Charged Hadrons
• Search for an H-dibaryon with mass near 2m_Lambda in Y(1S) and Y(2S) decays
• Determining the upper limit of Gamma_{ee} for the Y(4260)
• Searching for the Bottom Counterparts of X(3872) and Y(4260) via ${\pi }^{+}{\pi }^{-}{\rm Y}$
• Search for a new bottomonium state decaying to Upsilon(1S) pi+ pi- in pp collisions at sqrt(s) = 8 TeV
• Observation of two new $N^{\ast }$ resonances in $\psi (3686)\to p\bar{p}{\pi }^0$
• Study of Jψdecaying into ωp \bar p
• Measurement of the B -> Dbar(*)D(*)K branching fractions
• Experimental Review of Structures in the $J/\psi \varphi$ Mass Spectrum
• Measurement of Time-Dependent CP-Violating Parameters in B0 -> K0S K0S decays

Cited by in corpus (6)

• Influence of threshold effects induced by charmed meson rescattering
• Photoproduction of the charged charmoniumlike $Z_c^{+}(4200)$
• Isovector and hidden-beauty partners of the X(3872)
• Surveying the SO(10) Model Landscape: The Left-Right Symmetric Case
• States generated in the $K$-multi-$\rho$ interactions
• Unexpected Mesons X, Y, Z, ... (tetraquarks? hadron molecules? ...)