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v t e

In particle physics, a tetraquark is an exotic meson composed of four valence quarks. A tetraquark state has long been suspected to be allowed by quantum chromodynamics, the modern theory of strong interactions. A tetraquark state is an example of an exotic hadron which lies outside the conventional quark model classification. A number of different types of tetraquark have been observed.

History and discoveries

This article may be better presented in list format to meet Misplaced Pages's quality standards. Please help improve this article by converting it into a stand-alone or embedded list. (July 2022)

Several tetraquark candidates have been reported by particle physics experiments in the 21st century. The quark contents of these states are almost all qqQQ, where q represents a light (up, down or strange) quark, Q represents a heavy (charm or bottom) quark, and antiquarks are denoted with an overline. The existence and stability of tetraquark states with the qqQQ (or qqQQ) have been discussed by theoretical physicists for a long time, however these are yet to be reported by experiments.

Timeline

In 2003, a particle temporarily called X(3872), by the Belle experiment in Japan, was proposed to be a tetraquark candidate, as originally theorized. The name X is a temporary name, indicating that there are still some questions about its properties to be tested. The number following is the mass of the particle in MeV/c.

In 2004, the D_sJ(2632) state seen in Fermilab's SELEX was suggested as a possible tetraquark candidate.

In 2007, Belle announced the observation of the Z(4430) state, a
c

c

d

u
tetraquark candidate. There are also indications that the Y(4660), also discovered by Belle in 2007, could be a tetraquark state.

In 2009, Fermilab announced that they have discovered a particle temporarily called Y(4140), which may also be a tetraquark.

In 2010, two physicists from DESY and a physicist from Quaid-i-Azam University re-analyzed former experimental data and announced that, in connection with the
ϒ
(5S) meson (a form of bottomonium), a well-defined tetraquark resonance exists.

In June 2013, the BES III experiment in China and the Belle experiment in Japan independently reported on Z_c(3900), the first confirmed four-quark state.

In 2014, the Large Hadron Collider experiment LHCb confirmed the existence of the Z(4430) state with a significance of over 13.9 σ.

In February 2016, the DØ experiment reported evidence of a narrow tetraquark candidate, named X(5568), decaying to
B
_s
π
. In December 2017, DØ also reported observing the X(5568) using a different
B
_s final state. However, it was not observed in searches by the LHCb, CMS, CDF, or ATLAS experiments.

In June 2016, LHCb announced the discovery of three additional tetraquark candidates, called X(4274), X(4500) and X(4700).

In 2020, LHCb announced the discovery of a
c

c

c

c
tetraquark: X(6900). In 2022, ATLAS also observed X(6900), and in 2023, CMS reported an observation of three such states, X(6600), X(6900), and X(7300).

In 2021, LHCb announced the discovery of four additional tetraquarks, including ccus.

In 2022, LHCb announced the discovery of csud and csud.

See also

• Color confinement
• Double-charm tetraquark
• Hadron
• Pentaquark
• Tetraneutron

References

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16. V. M. Abazov; et al. (D0 collaboration) (2016). "Observation of a new
    B
    _s
    π
    state". Physical Review Letters. 117 (2): 022003. arXiv:1602.07588. Bibcode:2016PhRvL.117b2003A. doi:10.1103/PhysRevLett.117.022003. PMID 27447502. S2CID 7789961.
17. Abazov, V.M.; et al. (D0 collaboration) (2018). "Study of the X(5568) state with semileptonic decays of the B
    _s meson". Physical Review D. 97 (9): 092004. arXiv:1712.10176. Bibcode:2018PhRvD..97i2004A. doi:10.1103/PhysRevD.97.092004. S2CID 119337959.
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    _s π Invariant Mass Spectrum with the ATLAS Experiment". Physical Review Letters. 120 (20): 202007. arXiv:1802.01840. Bibcode:2018PhRvL.120t2007A. doi:10.1103/PhysRevLett.120.202007. PMID 29864314. S2CID 216915898.
22. Announcement by LHCb
23. R. Aaij; et al. (LHCb collaboration) (2017). "Observation of J/ψφ structures consistent with exotic states from amplitude analysis of B→J/ψφK decays". Physical Review Letters. 118 (2): 022003. arXiv:1606.07895. Bibcode:2017PhRvL.118b2003A. doi:10.1103/PhysRevLett.118.022003. PMID 28128595. S2CID 206284149.
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25. "Observation of a four-charm-quark tetraquark". LHCb - Large Hadron Collider beauty experiment. CERN. 1 July 2020. Retrieved 12 July 2020.
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27. "CMS Observes A Potential Family Of Tetra-Quark States Composed Only Of Charm Quarks". CMS. 22 March 2023. Retrieved 22 July 2024.
28. "LHCb discovers three new exotic particles". CERN. 5 July 2022. Retrieved 8 July 2022.

External links

• The Belle experiment (press release)
• O'Luanaigh, Cian. "LHCb confirms existence of exotic hadrons". cern.ch. Geneva, Switzerland: CERN. Retrieved 2014-04-12.

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