|Standard model of particle physics|
A tetraquark, in particle physics, is a hypothetical meson composed of four valence quarks. In principle, a tetraquark state may be allowed in quantum chromodynamics, the modern theory of strong interactions. However, there has been no confirmed report of a tetraquark state to date. Any established tetraquark state would be an example of an exotic hadron which lies outside the quark model classification.
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.
In 2004, the DsJ(2632) state seen in Fermilab's SELEX was suggested as a possible tetraquark candidate.
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.
- D. Harris (13 April 2008). "The charming case of X(3872)". Symmetry Magazine. Retrieved 2009-12-17.
- L. Maiani, F. Piccinini, V. Riquer and A.D. Polosa (2005). "Diquark-antidiquarks with hidden or open charm and the nature of X(3872)". Physical Review D 71: 014028. arXiv:hep-ph/0412098. Bibcode:2005PhRvD..71a4028M. doi:10.1103/PhysRevD.71.014028.
- G. Cotugno, R. Faccini, A.D. Polosa and C. Sabelli (2010). "Charmed Baryonium". Physical Review Letters 104 (13): 132005. arXiv:0911.2178. Bibcode:2010PhRvL.104m2005C. doi:10.1103/PhysRevLett.104.132005.
- A. Ali, C. Hambrock, M.J. Aslam (2010). "Tetraquark Interpretation of the BELLE Data on the Anomalous Υ(1S)π+π- and Υ(2S)π+π- Production near the Υ(5S) Resonance". Physical Review Letters 104 (16): 162001. arXiv:0912.5016. Bibcode:2010PhRvL.104p2001A. doi:10.1103/PhysRevLett.104.162001.
- Eric Swanson (2013). "Viewpoint: New Particle Hints at Four-Quark Matter". Physics 69 (6). doi:10.1103.
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