nLab tetraquark

Idea

A tetraquark is an exotic meson which is a bound state of four quarks, or rather: of a diquark and an anti-diquark.

Related concepts

• hadron supersymmetry

• XYZ meson

References

General

The idea of tetraquarks is mentioned already in the original articles on quarks.

The original proposal for tetraquarks with two heavy quark constitutents?:

• J.P. Ader, J.M. Richard, P. Taxil, Do narrow heavy multiquark states exist?, Phys. Rev. D 25 (1982) 2370 (doi:10.1103/PhysRevD.25.2370, spire:166170)

and fully heavy tetraquarks:

• L. Heller and J. A. Tjon, Bound states of heavyQ^2 Q^{-2}* systems, Phys. Rev. D 32 (1985) 755 (doi:10.1103/PhysRevD.32.755)

See also:

• Wikipedia, Tetraquark

Via hadron supersymmetry

Discussion in view of hadron supersymmetry and diquark-models:

in holographic light front QCD:

• Hans Günter Dosch, Stanley Brodsky, Guy de Teramond, Marina Nielsen, Liping Zou, Exotic States in a Holographic Theory, QCD 20) (arXiv:2012.02496)

in regards to experimental results:

• M. A. Bedolla, J. Ferretti, C. D. Roberts, E. Santopinto, Spectrum of fully-heavy tetraquarks from a diquark+antidiquark perspective (arXiv:1911.00960, doi:10.1140/epjc/s10052-020-08579-3)

Experimental detection

Fully charmed tetraquark

Experimental detection of a tetraquark resonance $X(6900)$ made entirely of four charm quarks and argued to be the first observed “true” tetraquark state (instead of just a “diquark molecule”):

• LHCb collaboration, Observation of structure in the $J/\psi$-pair mass spectrum, Science Bulletin 65 (2020) 1983 (arXiv:2006.16957, doi:10.1016/j.scib.2020.08.032, CERN news)

Popular exposition:

• Davide Castelvecchi, Exotic four-quark particle spotted at Large Hadron Collider, Nature News 10 Aug 2021 (doi:10.1038/d41586-021-02174-6)

Theoretical explanation:

• Ming-Sheng liu, Feng-Xiao Liu, Xian-Hui Zhong, Qiang Zhao, Full-heavy tetraquark states and their evidences in the LHCb di-J/ψ spectrum (arXiv:2006.11952)

• Qi-Fang Lü, Dian-Yong Chen, Yu-Bing Dong, Masses of fully heavy tetraquarks $Q Q \overline{Q} \overline{Q}$ in an extended relativized quark model, Eur. Phys. J. C 80, 871 (2020) (arXiv:2006.14445, doi:10.1140/epjc/s10052-020-08454-1)

reviewed in:

• Jean-Marc Richard, About the $J/\psi$ $J/\psi$ peak of LHCb: fully-charmed tetraquark?, Science Bulletin Volume 65, Issue 23, 15 December 2020, Pages 1954-1955 (arXiv:2008.01962, doi:10.1016/j.scib.2020.08.020)

• Jean-Marc Richard, Fully-heavy tetraquarks and other heavy multiquarks, Nuclear and Particle Physics Proceedings 00 (2021) 1–5 (arXiv:2105.02503)

$T^+_{c c}$ tetraquark

Indication of a tetraquark $c c \bar u \bar d$ with two charm quarks, and anti-up quark and an anti-down quark:

• LHCb collaboration, Observation of an exotic narrow doubly charmed tetraquark (arXiv:2109.01038)

• LHCb collaboration, Study of the doubly charmed tetraquark $T^+_{c c}$ (arXiv:2109.01056)

Further discussion:

• Sean Fleming, Reed Hodges, Thomas Mehen, $T_{c c}^+$ Decays: Differential Spectra and Two-Body Final States (arXiv:2109.02188)

• Huimin Ren, Fan Wu, Ruilin Zhu, Hadronic molecule interpretation of $T_{c c}^+$ and its beauty-partners (arXiv:2109.02531)