Tetraquark

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A tetraquark, in particle physics, is an exotic meson composed of four valence quarks. In principle, a tetraquark state may be allowed in quantum chromodynamics,[1] the modern theory of strong interactions. Any established tetraquark state would be an example of an exotic hadron which lies outside the quark model classification.[qualify evidence]

History[edit]

Colour flux tubes produced by four static quark and antiquark charges, computed in lattice QCD.[2] Confinement in Quantum Chromo Dynamics leads to the production of flux tubes connecting colour charges. The flux tubes act as attractive QCD string-like potentials.

In 2003 a particle temporarily called X(3872), by the Belle experiment in Japan, was proposed to be a tetraquark candidate,[3] as originally theorized.[4] 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/c2.

In 2004, the DsJ(2632) state seen in Fermilab's SELEX was suggested as a possible tetraquark candidate.[citation needed]

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.[5]

In 2009, Fermilab announced that they have discovered a particle temporarily called Y(4140), which may also be a tetraquark.[6]

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.[7][8]

In June 2013, the BES III experiment in China and the Belle experiment in Japan independently reported on Zc(3900), the first confirmed four-quark state.[9]

In 2014, the Large Hadron Collider experiment LHCb confirmed the existence of the Z(4430) state with a significance of over 13.9 σ.[10][11]

In February 2016, the DØ experiment announced the observation of a narrow tetraquark candidate, named X(5568), decaying to Bsπ±.[12] However, preliminary results from LHCb, presented at the 51st Rencontres de Moriond Electroweak session, show no evidence for the state, despite a much larger sample of
B0
s
π± candidates.[13]

In June 2016, LHCb announced the discovery of three additional tetraquark candidates, called X(4274), X(4500) and X(4700).[14][15][16]

See also[edit]

References[edit]

  1. ^ U. Kulshreshtha; D. S. Kulshreshtha; J. P. Vary (2015). "Hamiltonian, Path Integral and BRST Formulations of Large N Scalar $QCD_{2}$ on the Light-Front and Spontaneous Symmetry Breaking". Eur. Phys. J. C. 75 (4): 174. arXiv:1503.06177Freely accessible. Bibcode:2015EPJC...75..174K. doi:10.1140/epjc/s10052-015-3377-x. 
  2. ^ N. Cardoso; M. Cardoso; P. Bicudo (2011). "Colour Fields Computed in SU(3) Lattice QCD for the Static Tetraquark System". Physical Review D. 84 (5): 054508. arXiv:1107.1355Freely accessible. Bibcode:2011PhRvD..84e4508C. doi:10.1103/PhysRevD.84.054508. 
  3. ^ D. Harris (13 April 2008). "The charming case of X(3872)". Symmetry Magazine. Retrieved 2009-12-17. 
  4. ^ L. Maiani; F. Piccinini; V. Riquer; A.D. Polosa (2005). "Diquark-antidiquarks with hidden or open charm and the nature of X(3872)". Physical Review D. 71 (1): 014028. arXiv:hep-ph/0412098Freely accessible. Bibcode:2005PhRvD..71a4028M. doi:10.1103/PhysRevD.71.014028. 
  5. ^ G. Cotugno; R. Faccini; A.D. Polosa; C. Sabelli (2010). "Charmed Baryonium". Physical Review Letters. 104 (13): 132005. arXiv:0911.2178Freely accessible. Bibcode:2010PhRvL.104m2005C. doi:10.1103/PhysRevLett.104.132005. 
  6. ^ A. Minard (18 March 2009). "New Particle Throws Monkeywrench in Particle Physics". Universe Today. Retrieved 2014-04-12. 
  7. ^ Z. Matthews (27 April 2010). "Evidence grows for tetraquarks". Physics World. Retrieved 2014-04-12. 
  8. ^ 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:0912.5016Freely accessible. Bibcode:2010PhRvL.104p2001A. doi:10.1103/PhysRevLett.104.162001. 
  9. ^ E. Swanson (2013). "Viewpoint: New Particle Hints at Four-Quark Matter". Physics. 6: 69. Bibcode:2013PhyOJ...6...69S. doi:10.1103/Physics.6.69. 
  10. ^ C. O'Luanaigh (9 Apr 2014). "LHCb confirms existence of exotic hadrons". CERN. Retrieved 2016-04-04. 
  11. ^ R. Aaij; et al. (LHCb collaboration) (2014). "Observation of the resonant character of the Z(4430)− state". Physical Review Letters. 112: 222002. arXiv:1404.1903Freely accessible. Bibcode:2014PhRvL.112v2002A. doi:10.1103/PhysRevLett.112.222002. PMID 24949760. 
  12. ^ V. M. Abazov; et al. (DØ collaboration) (2016). "Observation of a new
    B0
    s
    π± state". arXiv:1602.07588Freely accessible [hep-ex].
     
  13. ^ J. van Tilburg (13 March 2016). "Recent hot results & semileptonic b hadron decay" (PDF). CERN. Retrieved 2016-04-04. 
  14. ^ Announcement by LHCb
  15. ^ R. Aaij; et al. (LHCb collaboration) (2016). "Observation of J/ψφ structures consistent with exotic states from amplitude analysis of B+→J/ψφK+ decays". arXiv:1606.07895Freely accessible [hep-ex]. 
  16. ^ R. Aaij; et al. (LHCb collaboration) (2016). "Amplitude analysis of B+→J/ψφK+ decays". arXiv:1606.07898Freely accessible [hep-ex]. 

External links[edit]