Heavy quarkonium: progress, puzzles, and opportunities

In the past decade many charmonium-like states were observed experimentally. Especially those charged charmoniumlike Z c states and bottomonium-like Z b states can not be accommodated within the naive quark model. These charged Z c states are good candidates of either the hidden-charm tetraquark states or molecules composed of a pair of charmed mesons. Recently, the LHCb Collaboration discovered two hidden-charm pentaquark states, which are also beyond the quark model. In this work, we review the current experimental progress and investigate various theoretical interpretations of these candidates of the multiquark states. We list the puzzles and theoretical challenges of these models when confronted with the experimental data. We also discuss possible future measurements which may distinguish the theoretical schemes on the underlying structures of the hidden-charm multiquark states.

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“…Interested readers may also consult reviews in Refs. [40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,39].…”

Section: General Status Of Hadron Spectroscopymentioning

confidence: 99%

The hidden-charm pentaquark and tetraquark states

et al. 2016

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“…In any case, M µ 5 and M µ 6 drop out in photoproduction where the remaining amplitudes are kinematically safe. Note also that A 3,5,6 are antisymmetric in λ and therefore they vanish for λ = 0.…”

Section: (24)mentioning

confidence: 99%

“…Then, the Hamiltonian is comprised of a kinetic part describing these constituents together with a potential for the inter-quark forces. Non-relativistically this has the form 5) where m i are the constituent quark masses as parameters of the model, p i the momenta and r i the individual quark coordinates. The simplest prototypical example of a confining potential is that of a harmonic oscillator where the quark-quark potential is of the form 6) i.e., a sum of two-body confining potentials where r ij = r i − r j , r ij = |r ij | and K is some constant.…”

Section: The Quark Modelmentioning

confidence: 99%

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Baryons as relativistic three-quark bound states

Eichmann

Sanchis-Alepuz

Williams

et al. 2016

Progress in Particle and Nuclear Physics

435

530

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We review the spectrum and electromagnetic properties of baryons described as relativistic three-quark bound states within QCD. The composite nature of baryons results in a rich excitation spectrum, whilst leading to highly non-trivial structural properties explored by the coupling to external (electromagnetic and other) currents. Both present many unsolved problems despite decades of experimental and theoretical research. We discuss the progress in these fields from a theoretical perspective, focusing on nonperturbative QCD as encoded in the functional approach via Dyson-Schwinger and Bethe-Salpeter equations. We give a systematic overview as to how results are obtained in this framework and explain technical connections to lattice QCD. We also discuss the mutual relations to the quark model, which still serves as a reference to distinguish 'expected' from 'unexpected' physics. We confront recent results on the spectrum of non-strange and strange baryons, their form factors and the issues of two-photon processes and Compton scattering determined in the DysonSchwinger framework with those of lattice QCD and the available experimental data. The general aim is to identify the underlying physical mechanisms behind the plethora of observable phenomena in terms of the underlying quark and gluon degrees of freedom.

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“…In the last few years we are witnessing the discovery of a number of new narrow hadronic resonances with charm which do not match standard quark-antiquark interpretation, thereby named exotic hadrons [2]. This has called for alternative interpretations of their inner structure.…”

Section: Introductionmentioning

confidence: 99%

Search for charmonium and exotics above DD-bar threshold in PANDA experiment at FAIR

Barabanov¹

2013

Proceedings of XXI International Baldin Seminar on High Energy Physics Problems — PoS(Baldin ISHEPP XXI)

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The spectroscopy of charmonium and exotics is discussed. It is a good testing tool for the theories of strong interactions, including: QCD in both the perturbative and nonperturbative regimes, LQCD, potential models and phenomenological models. For this purpose an elaborated analysis of the charmonium, charmed hybrids and tetraqurks spectra is given, and attempts to interpret recent experimental data in the above D D threshold region are considered. Experiments using antiproton beams take advantage of the intensive production of particle-antiparticle pairs in antiproton-proton annihilations. Experimental data from different collaborations are analyzed with special attention given to new states with hidden charm that were discovered recently. Some of these states can be interpreted as higher-laying S, P & D wave charmonium states and tetraquarks with a hidden charm. But much more data on different decay modes are needed before firmer conclusions can be made. These data can be derived directly from the experiments using a high quality antiproton beam with momenta ranging from 1 GeV/c to 15 GeV/c.

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Heavy quarkonium: progress, puzzles, and opportunities

Cited by 1,543 publications

References 694 publications

The hidden-charm pentaquark and tetraquark states

The hidden-charm pentaquark and tetraquark states

Baryons as relativistic three-quark bound states

Search for charmonium and exotics above DD-bar threshold in PANDA experiment at FAIR

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