Tetraquark

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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, [1] 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. [2] [3]

Contents

History and discoveries

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. [4]

Colour flux tubes produced by four static quark and antiquark charges, computed in lattice QCD. Confinement in quantum chromodynamics leads to the production of flux tubes connecting colour charges. The flux tubes act as attractive QCD string-like potentials. TQ EB ape hyp r1 8 r2 14 Act 3D Sim.jpg
Colour flux tubes produced by four static quark and antiquark charges, computed in lattice QCD. Confinement in quantum chromodynamics leads to the production of flux tubes connecting colour charges. The flux tubes act as attractive QCD string-like potentials.
Timeline

In 2003, a particle temporarily called X(3872), by the Belle experiment in Japan, was proposed to be a tetraquark candidate, [6] as originally theorized. [7] 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. [8]

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. [9]

In 2009, Fermilab announced that they have discovered a particle temporarily called Y(4140), which may also be a tetraquark. [10]

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. [11] [12]

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. [13]

In 2014, the Large Hadron Collider experiment LHCb confirmed the existence of the Z(4430) state with a significance of over 13.9 σ. [14] [15]

In February 2016, the DØ experiment reported evidence of a narrow tetraquark candidate, named X(5568), decaying to
B0
s
π±
. [16] In December 2017, DØ also reported observing the X(5568) using a different
B0
s final state. [17] However, it was not observed in searches by the LHCb, [18] CMS, [19] CDF, [20] or ATLAS [21] experiments.

In June 2016, LHCb announced the discovery of three additional tetraquark candidates, called X(4274), X(4500) and X(4700). [22] [23] [24]

In 2020, LHCb announced the discovery of a
c
c
c
c
 tetraquark: X(6900). [2] [25] In 2022, ATLAS also observed X(6900), [26] and in 2023, CMS reported an observation of three such states, X(6600), X(6900), and X(7300). [27]

In 2021, LHCb announced the discovery of four additional tetraquarks, including ccus. [3]

In 2022, LHCb announced the discovery of csud and csud. [28]

See also

Related Research Articles

<span class="mw-page-title-main">Hadron</span> Composite subatomic particle

In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules, which are held together by the electric force. Most of the mass of ordinary matter comes from two hadrons: the proton and the neutron, while most of the mass of the protons and neutrons is in turn due to the binding energy of their constituent quarks, due to the strong force.

<span class="mw-page-title-main">Omega baryon</span> Subatomic hadron particle

Omega baryons are a family of subatomic hadrons which are represented by the symbol
Ω
 and are either charge neutral or have a +2, +1 or −1 elementary charge. Additionally, they contain no up or down quarks. Omega baryons containing top quarks are also not expected to be observed. This is because the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s, which is about a twentieth of the timescale necessary for the strong interactions required for Hadronization, the process by which hadrons form from quarks and gluons.

<span class="mw-page-title-main">Charm quark</span> Type of quark

The charm quark, charmed quark, or c quark is an elementary particle found in composite subatomic particles called hadrons such as the J/psi meson and the charmed baryons created in particle accelerator collisions. Several bosons, including the W and Z bosons and the Higgs boson, can decay into charm quarks. All charm quarks carry charm, a quantum number. This second-generation particle is the third-most-massive quark, with a mass of 1.27±0.02 GeV/c2 as measured in 2022, and a charge of +⁠2/3⁠ e.

<span class="mw-page-title-main">Pentaquark</span> Human-made subatomic particle

A pentaquark is a human-made subatomic particle, consisting of four quarks and one antiquark bound together; they are not known to occur naturally, or exist outside of experiments specifically carried out to create them.

In particle physics, the baryon number is a strictly conserved additive quantum number of a system. It is defined as where ⁠⁠ is the number of quarks, and ⁠⁠ is the number of antiquarks. Baryons have a baryon number of +1, mesons have a baryon number of 0, and antibaryons have a baryon number of −1. Exotic hadrons like pentaquarks and tetraquarks are also classified as baryons and mesons depending on their baryon number.

<span class="mw-page-title-main">Exotic baryon</span> Subatomic particles; baryons with atypical quark content

In particle physics, exotic baryons are a type of hadron with half-integer spin, but with a quark content different from the three quarks (qqq) present in conventional baryons. An example would be pentaquarks, consisting of four quarks and one antiquark (qqqqq̅).

<span class="mw-page-title-main">Exotic meson</span> Meson particles which do not fit into the quark model

In particle physics, exotic mesons are mesons that have quantum numbers not possible in the quark model; some proposals for non-standard quark model mesons could be:

<span class="mw-page-title-main">LHCb experiment</span> Experiment at the Large Hadron Collider

The LHCb experiment is a particle physics detector experiment collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designed primarily to measure the parameters of CP violation in the interactions of b-hadrons. Such studies can help to explain the matter-antimatter asymmetry of the Universe. The detector is also able to perform measurements of production cross sections, exotic hadron spectroscopy, charm physics and electroweak physics in the forward region. The LHCb collaborators, who built, operate and analyse data from the experiment, are composed of approximately 1650 people from 98 scientific institutes, representing 22 countries. Vincenzo Vagnoni succeeded on July 1, 2023 as spokesperson for the collaboration from Chris Parkes. The experiment is located at point 8 on the LHC tunnel close to Ferney-Voltaire, France just over the border from Geneva. The (small) MoEDAL experiment shares the same cavern.

<span class="mw-page-title-main">Quarkonium</span> Meson whose constituents are a quark and its own antiquark of the same flavor

In particle physics, quarkonium is a flavorless meson whose constituents are a heavy quark and its own antiquark, making it both a neutral particle and its own antiparticle. The name "quarkonium" is analogous to positronium, the bound state of electron and anti-electron. The particles are short-lived due to matter-antimatter annihilation.

<span class="mw-page-title-main">Exotic hadron</span> Subatomic particles consisting of quarks and gluons

Exotic hadrons are subatomic particles composed of quarks and gluons, but which – unlike "well-known" hadrons such as protons, neutrons and mesons – consist of more than three valence quarks. By contrast, "ordinary" hadrons contain just two or three quarks. Hadrons with explicit valence gluon content would also be considered exotic. In theory, there is no limit on the number of quarks in a hadron, as long as the hadron's color charge is white, or color-neutral.

<span class="mw-page-title-main">DØ experiment</span> Particle physics research project (1983–2011)

The DØ experiment was a worldwide collaboration of scientists conducting research on the fundamental nature of matter. DØ was one of two major experiments located at the Tevatron Collider at Fermilab in Batavia, Illinois. The Tevatron was the world's highest-energy accelerator from 1983 until 2009, when its energy was surpassed by the Large Hadron Collider. The DØ experiment stopped taking data in 2011, when the Tevatron shut down, but data analysis is still ongoing. The DØ detector is preserved in Fermilab's DØ Assembly Building as part of a historical exhibit for public tours.

The Xi baryons or cascade particles are a family of subatomic hadron particles which have the symbol Ξ and may have an electric charge of +2 e, +1 e, 0, or −1 e, where e is the elementary charge.

<span class="mw-page-title-main">Strange B meson</span>

The
B
s meson is a meson composed of a bottom antiquark and a strange quark. Its antiparticle is the
B
s meson, composed of a bottom quark and a strange antiquark.

The X(3872) is an exotic meson candidate with a mass of 3871.68 MeV/c2 which does not fit into the quark model. It was first discovered in 2003 by the Belle experiment in Japan and later confirmed by several other experimental collaborations. Several theories have been proposed for its nature, such as a mesonic molecule or a diquark-antidiquark pair (tetraquark).

Z(4430) is a mesonic resonance discovered by the Belle experiment. It has a mass of 4430 MeV/c2. The resonant nature of the peak has been confirmed by the LHCb experiment with a significance of at least 13.9 σ. The particle is charged and is thought to have a quark content of
c

c

d

u
, making it a tetraquark candidate. It has the spin-parity quantum numbers JP = 1+.

In particle physics, B mesons are mesons composed of a bottom antiquark and either an up, down, strange or charm quark. The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime. The combination of a bottom antiquark and a bottom quark is not a B meson, but rather bottomonium, which is something else entirely.

The D mesons are the lightest particle containing charm quarks. They are often studied to gain knowledge on the weak interaction. The strange D mesons (Ds) were called "F mesons" prior to 1986.

The Y(4140) particle is an electrically neutral exotic hadron candidate that is about 4.4 times heavier than the proton. It was observed at Fermilab and announced on 17 March 2009. This particle is extremely rare and was detected in only 20 of billions of collisions.

The Zc(3900) is a hadron, a type of subatomic particle made of quarks, believed to be the first tetraquark that has been observed experimentally. The discovery was made in 2013 by two independent research groups: one using the BES III detector at the Chinese Beijing Electron Positron Collider, the other being part of the Belle experiment group at the Japanese KEK particle physics laboratory.

<span class="mw-page-title-main">Sheldon Stone</span> American particle physicist (1946–2021)

Sheldon Leslie Stone was a distinguished professor of physics at Syracuse University. He is best known for his work in experimental elementary particle physics, the Large Hadron Collider beauty experiment (LHCb), and B decays. He made significant contributions in the areas of data analysis, LHCb detector design and construction, and phenomenology.

References

  1. ↑ U. Kulshreshtha; D. S. Kulshreshtha; J. P. Vary (2015). "Hamiltonian, path integral and BRST formulations of large N scalar QCD2 on the light-front and spontaneous symmetry breaking". European Physical Journal C . 75 (4): 174. arXiv: 1503.06177 . Bibcode:2015EPJC...75..174K. doi:10.1140/epjc/s10052-015-3377-x. S2CID   119102254.
  2. 1 2 R. Aaij; et al. (LHCb collaboration) (2020). "Observation of structure in the J/ψ-pair mass spectrum". Science Bulletin. 65 (23): 1983–1993. arXiv: 2006.16957 . Bibcode:2020SciBu..65.1983L. doi:10.1016/j.scib.2020.08.032. PMID   36659056. S2CID   220265852.
  3. 1 2 LHCb collaboration; Aaij, R.; Beteta, C. Abellán; Ackernley, T.; Adeva, B.; Adinolfi, M.; Afsharnia, H.; Aidala, C. A.; Aiola, S.; Ajaltouni, Z.; Akar, S. (2021-03-02). "Observation of New Resonances Decaying to J/ψK+ and J/ψϕ". Physical Review Letters. 127 (8): 082001. arXiv: 2103.01803 . Bibcode:2021PhRvL.127h2001A. doi:10.1103/PhysRevLett.127.082001. PMID   34477418. S2CID   232092368.
  4. ↑ Si-Qiang, Luo; Kan, Chen; Xiang, Liu; Yan-Rui, Liu; Shi-Lin, Zhu (25 October 2017). "Exotic tetraquark states with the qqQQ configuration" (PDF). European Physical Journal C. 77:709 (10). doi: 10.1140/epjc/s10052-017-5297-4 . S2CID   119377466 . Retrieved 26 November 2017.
  5. ↑ "The charming case of X(3872) (APS April 2008) | symmetry magazine". www.symmetrymagazine.org. 2008-04-13. Retrieved 2023-11-09.
  6. ↑ D. Harris (13 April 2008). "The charming case of X(3872)". Symmetry Magazine . Retrieved 2009-12-17.
  7. ↑ 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/0412098 . Bibcode:2005PhRvD..71a4028M. doi:10.1103/PhysRevD.71.014028. S2CID   119345314.
  8. ↑ Kulshreshtha, Usha; Daya Shankar Kulshreshtha; Vary, James P. (2005). "Regge Trajectories Analysis to D⋆
    SJ    (2317)±, DSJ(2460)± and DSJ(2632)+ Mesons". Physical Review D . 72: 017902. arXiv: hep-ph/0408124 . doi:10.1103/PhysRevD.72.017902. S2CID   10124970.
  9. ↑ G. Cotugno; R. Faccini; A.D. Polosa; C. Sabelli (2010). "Charmed Baryonium". Physical Review Letters . 104 (13): 132005. arXiv: 0911.2178 . Bibcode:2010PhRvL.104m2005C. doi:10.1103/PhysRevLett.104.132005. PMID   20481876. S2CID   353652.
  10. ↑ A. Minard (18 March 2009). "New Particle Throws Monkeywrench in Particle Physics". Universe Today . Retrieved 2014-04-12.
  11. ↑ Z. Matthews (27 April 2010). "Evidence grows for tetraquarks". Physics World . Archived from the original on 2011-11-09. Retrieved 2014-04-12.
  12. ↑ 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. PMID   20482041.
  13. ↑ E. Swanson (2013). "Viewpoint: New Particle Hints at Four-Quark Matter". Physics . 6: 69. Bibcode:2013PhyOJ...6...69S. doi: 10.1103/Physics.6.69 .
  14. ↑ C. O'Luanaigh (9 Apr 2014). "LHCb confirms existence of exotic hadrons". CERN . Retrieved 2016-04-04.
  15. ↑ R. Aaij; et al. (LHCb collaboration) (2014). "Observation of the resonant character of the Z(4430)− state". Physical Review Letters . 112 (22): 222002. arXiv: 1404.1903 . Bibcode:2014PhRvL.112v2002A. doi:10.1103/PhysRevLett.112.222002. PMID   24949760. S2CID   904429.
  16. ↑ V. M. Abazov; et al. (D0 collaboration) (2016). "Observation of a new
    B0
    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 B0
    s     meson". Physical Review D. 97 (9): 092004. arXiv: 1712.10176 . Bibcode:2018PhRvD..97i2004A. doi:10.1103/PhysRevD.97.092004. S2CID   119337959.
  18. ↑ J. van Tilburg (13 March 2016). "Recent hot results & semileptonic b hadron decay" (PDF). CERN . Retrieved 2016-04-04.
  19. ↑ Sirunyan, A. M.; et al. (CMS Collaboration) (2018). "Search for the X(5568) State Decaying into B0
    s    π± in Proton-Proton Collisions at √s =8  TeV". Physical Review Letters. 120 (20): 202005. arXiv: 1712.06144 . doi:10.1103/PhysRevLett.120.202005. PMID   29864318. S2CID   119402891.
  20. ↑ Aaltonen, T.; et al. (CDF Collaboration) (2018). "A search for the exotic meson X(5568) with the Collider Detector at Fermilab". Physical Review Letters. 120 (20): 202006. arXiv: 1712.09620 . Bibcode:2018PhRvL.120t2006A. doi:10.1103/PhysRevLett.120.202006. PMID   29864341. S2CID   43934060.
  21. ↑ Aaboud, M.; et al. (ATLAS Collaboration) (2018). "Search for a Structure in the B0
    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.
  24. ↑ R. Aaij; et al. (LHCb collaboration) (2017). "Amplitude analysis of B+→J/ψφK+ decays". Physical Review D. 95 (1): 012002. arXiv: 1606.07898 . Bibcode:2017PhRvD..95a2002A. doi:10.1103/PhysRevD.95.012002. S2CID   73689011.
  25. ↑ "Observation of a four-charm-quark tetraquark". LHCb - Large Hadron Collider beauty experiment . CERN. 1 July 2020. Retrieved 12 July 2020.
  26. ↑ "ATLAS observes potential four-charm tetraquark". ATLAS. 9 July 2022. Retrieved 2022-07-21.
  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.
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