tetraquark
{{Short description|Exotic meson composed of four valence quarks}}
{{Standard model of particle physics}}
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,{{ cite journal|author1=U. Kulshreshtha|author2=D. S. Kulshreshtha|author3=J. P. Vary|title= Hamiltonian, path integral and BRST formulations of large N scalar QCD2 on the light-front and spontaneous symmetry breaking|journal=European Physical Journal C|volume= 75|issue= 4|page= 174|year=2015|doi=10.1140/epjc/s10052-015-3377-x|arxiv=1503.06177|bibcode=2015EPJC...75..174K|s2cid=119102254 }} the modern theory of strong interactions. A tetraquark state is an example of an exotic hadron that lies outside the conventional quark model classification. A number of different types of tetraquark have been observed.
History and discoveries
{{Create list|date=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 q{{overline|q}}Q{{overline|Q}}, 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 qq{{overline|Q}}{{overline|Q}} (or {{overline|q}}{{overline|q}}QQ) have been discussed by theoretical physicists for a long time, however these are yet to be reported by experiments.{{cite journal|last1=Si-Qiang|first1=Luo|last2=Kan|first2=Chen|last3=Xiang|first3=Liu|last4=Yan-Rui|first4=Liu|last5=Shi-Lin|first5=Zhu|title=Exotic tetraquark states with the qq{{overline|Q}}{{overline|Q}} configuration|journal=European Physical Journal C|date=25 October 2017|volume=77:709|issue=10|url=https://link.springer.com/content/pdf/10.1140%2Fepjc%2Fs10052-017-5297-4.pdf|access-date=26 November 2017|doi=10.1140/epjc/s10052-017-5297-4|s2cid=119377466|doi-access=free}}
File:TQ EB ape hyp r1 8 r2 14 Act 3D Sim.jpg.{{Cite web |date=2008-04-13 |title=The charming case of X(3872) (APS April 2008) {{!}} symmetry magazine |url=https://www.symmetrymagazine.org/breaking/2008/04/13/the-charming-case-of-x3872?language_content_entity=und |access-date=2023-11-09 |website=www.symmetrymagazine.org |language=en}} 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,
{{cite web
|author=D. Harris
|date=13 April 2008
|title=The charming case of X(3872)
|url=http://www.symmetrymagazine.org/breaking/2008/04/13/the-charming-case-of-x3872/
|work=Symmetry Magazine
|access-date=2009-12-17
{{cite journal
|author1=L. Maiani
|author2=F. Piccinini
|author3=V. Riquer
|author4=A.D. Polosa
|year=2005
|title=Diquark-antidiquarks with hidden or open charm and the nature of X(3872)
|journal=Physical Review D
|volume=71|issue=1|page=014028
|arxiv=hep-ph/0412098
|bibcode=2005PhRvD..71a4028M
|doi=10.1103/PhysRevD.71.014028
|s2cid=119345314
}} 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 {{val|ul=MeV/c2}}.
In 2004, the DsJ(2632) state seen in Fermilab's SELEX was suggested as a possible tetraquark candidate.{{Cite journal|arxiv = hep-ph/0408124|last1 = Kulshreshtha|first1 = Usha|title = Regge Trajectories Analysis to D{{su|p=⋆|b=SJ}}(2317)±, DSJ(2460)± and DSJ(2632)+ Mesons|journal = Physical Review D|volume = 72|pages = 017902|author2 = Daya Shankar Kulshreshtha|last3 = Vary|first3 = James P.|year = 2005|doi = 10.1103/PhysRevD.72.017902|s2cid=10124970 }}
In 2007, Belle announced the observation of the Z(4430) state, a {{Subatomic particle|Charm quark|link=yes}}{{Subatomic particle|Charm antiquark|link=yes}}{{Subatomic particle|Down quark|link=yes}}{{Subatomic particle|Up antiquark|link=yes}} tetraquark candidate. There are also indications that the Y(4660), also discovered by Belle in 2007, could be a tetraquark state.
{{cite journal
|author1=G. Cotugno
|author2=R. Faccini
|author3=A.D. Polosa
|author4=C. Sabelli
|year=2010
|title=Charmed Baryonium
|journal=Physical Review Letters
|volume=104|issue=13|page=132005
|arxiv=0911.2178
|bibcode=2010PhRvL.104m2005C
|doi=10.1103/PhysRevLett.104.132005
|pmid=20481876
|s2cid=353652
}}
In 2009, Fermilab announced that they have discovered a particle temporarily called Y(4140), which may also be a tetraquark.
{{cite web
|author=A. Minard
|date=18 March 2009
|url=http://www.universetoday.com/2009/03/18/new-particle-throws-monkeywrench-in-particle-physics/
|title=New Particle Throws Monkeywrench in Particle Physics
|work=Universe Today
|access-date=2014-04-12
}}
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 Upsilon meson (a form of bottomonium), a well-defined tetraquark resonance exists.{{cite web
|author=Z. Matthews
|date=27 April 2010
|title=Evidence grows for tetraquarks
|url=http://physicsworld.com/cws/article/news/42475
|work=Physics World
|access-date=2014-04-12
|archive-date=2011-11-09
|archive-url=https://web.archive.org/web/20111109013800/http://physicsworld.com/cws/article/news/42475
|url-status=dead
{{cite journal
|author1=A. Ali
|author2=C. Hambrock
|author3=M.J. Aslam
|year=2010
|title=Tetraquark Interpretation of the BELLE Data on the Anomalous Υ(1S)π+π− and Υ(2S)π+π− Production near the Υ(5S) Resonance
|journal=Physical Review Letters
|volume=104|issue=16|page=162001
|arxiv=0912.5016
|bibcode=2010PhRvL.104p2001A
|doi=10.1103/PhysRevLett.104.162001
|pmid=20482041
}}
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.
{{cite journal
|author=E. Swanson
|year=2013
|title=Viewpoint: New Particle Hints at Four-Quark Matter
|journal=Physics
|volume=6|page=69
|bibcode=2013PhyOJ...6...69S
|doi=10.1103/Physics.6.69
|doi-access=free
}}
In 2014, the Large Hadron Collider experiment LHCb confirmed the existence of the Z(4430) state with a significance of over 13.9 σ.
{{cite web
|author=C. O'Luanaigh
|date=9 Apr 2014
|title=LHCb confirms existence of exotic hadrons
|url=http://home.web.cern.ch/about/updates/2014/04/lhcb-confirms-existence-exotic-hadrons
|publisher=CERN
|access-date=2016-04-04
{{cite journal
|author1=R. Aaij
|display-authors=etal
|collaboration=LHCb collaboration
|year=2014
|title=Observation of the resonant character of the Z(4430)− state
|journal=Physical Review Letters
|arxiv=1404.1903
|bibcode=2014PhRvL.112v2002A
|doi=10.1103/PhysRevLett.112.222002
|volume=112
|issue=22
|pmid=24949760
|page=222002
|s2cid=904429
}}
In February 2016, the DØ experiment reported evidence of a narrow tetraquark candidate, named X(5568), decaying to {{Subatomic particle|strange b0|link=yes}}{{SubatomicParticle|Pion+-}}.
{{cite journal
|author1=V. M. Abazov
|display-authors=etal
|collaboration=D0 collaboration
|year=2016
|title=Observation of a new {{Subatomic particle|strange b0}}{{SubatomicParticle|Pion+-}} state
|arxiv=1602.07588
|doi=10.1103/PhysRevLett.117.022003
|pmid=27447502
|volume=117
|issue=2
|pages=022003
|journal=Physical Review Letters
|bibcode=2016PhRvL.117b2003A
|s2cid=7789961
}}
In December 2017, DØ also reported observing the X(5568) using a different {{Subatomic particle|strange b0}} final state.{{Cite journal|arxiv = 1712.10176|last1 =Abazov|first1 = V.M.|collaboration=D0 collaboration|title = Study of the X±(5568) state with semileptonic decays of the B{{su|p=0|b=s}} meson|journal = Physical Review D|volume = 97|issue = 9|pages = 092004|year = 2018|doi = 10.1103/PhysRevD.97.092004|bibcode =2018PhRvD..97i2004A|s2cid =119337959|display-authors =etal}}
However, it was not observed in searches by the LHCb,
{{cite web
|author1=J. van Tilburg
|date=13 March 2016
|title=Recent hot results & semileptonic b hadron decay
|url=http://lhcb-public.web.cern.ch/lhcb-public/Images2016/VanTilburg.pdf
|publisher=CERN
|access-date=2016-04-04
}} CMS,{{Cite journal|arxiv = 1712.06144|last1 =Sirunyan|first=A. M.|collaboration=CMS Collaboration|title = Search for the X(5568) State Decaying into B{{su|p=0|b=s}}π± in Proton-Proton Collisions at √s =8 TeV|journal = Physical Review Letters|volume = 120|issue = 20|pages = 202005|year = 2018|doi = 10.1103/PhysRevLett.120.202005|pmid = 29864318|s2cid =119402891|display-authors =etal}} CDF,{{Cite journal|arxiv = 1712.09620|last1 =Aaltonen|first1 = T.|collaboration=CDF Collaboration|title = A search for the exotic meson X(5568) with the Collider Detector at Fermilab|journal = Physical Review Letters|volume = 120|issue = 20|pages = 202006|year = 2018|doi = 10.1103/PhysRevLett.120.202006|pmid = 29864341|bibcode =2018PhRvL.120t2006A|s2cid =43934060|display-authors =etal}} or ATLAS{{Cite journal|arxiv = 1802.01840|last1 =Aaboud|first1 = M.|collaboration=ATLAS Collaboration|title = Search for a Structure in the B{{su|p=0|b=s}} π± Invariant Mass Spectrum with the ATLAS Experiment|journal = Physical Review Letters|volume = 120|issue = 20|pages = 202007|year = 2018|doi = 10.1103/PhysRevLett.120.202007|pmid = 29864314|bibcode =2018PhRvL.120t2007A|s2cid =216915898|display-authors = etal}} experiments.
In June 2016, LHCb announced the discovery of three additional tetraquark candidates, called X(4274), X(4500) and X(4700).[http://lhcb-public.web.cern.ch/lhcb-public/#JpsiPhiExotics Announcement by LHCb]
{{cite journal
|author1=R. Aaij
|display-authors=etal
|collaboration=LHCb collaboration
|year=2017
|title=Observation of J/ψφ structures consistent with exotic states from amplitude analysis of B{{sup|+}}→J/ψφK{{sup|+}} decays
|arxiv=1606.07895
|doi=10.1103/PhysRevLett.118.022003
|pmid=28128595
|volume=118
|issue=2
|pages=022003
|journal=Physical Review Letters
|bibcode=2017PhRvL.118b2003A
|s2cid=206284149
{{cite journal
|author1=R. Aaij
|display-authors=etal
|collaboration=LHCb collaboration
|year=2017
|title=Amplitude analysis of B{{sup|+}}→J/ψφK{{sup|+}} decays
|arxiv=1606.07898
|doi=10.1103/PhysRevD.95.012002
|volume=95
|issue=1
|pages=012002
|journal=Physical Review D
|bibcode=2017PhRvD..95a2002A
|s2cid=73689011
}}
In 2020, LHCb announced the discovery of a
{{Subatomic particle|Charm quark|link=yes}}{{Subatomic particle|Charm quark|link=yes}}{{Subatomic particle|Charm antiquark|link=yes}}{{Subatomic particle|Charm antiquark|link=yes}}
{{cite journal
|author1=R. Aaij
|display-authors=etal
|collaboration=LHCb collaboration
|year=2020
|title=Observation of structure in the J/ψ-pair mass spectrum
|journal=Science Bulletin
|volume=65
|issue=23
|pages=1983–1993
|doi=10.1016/j.scib.2020.08.032
|pmid=36659056
|arxiv=2006.16957
|bibcode=2020SciBu..65.1983L
|s2cid=220265852
{{cite web
|date=1 July 2020
|title=Observation of a four-charm-quark tetraquark.
|url=https://lhcb-public.web.cern.ch/Welcome.html#Tcccc
|work=LHCb - Large Hadron Collider beauty experiment
|publisher=CERN
|access-date=12 July 2020
}} In 2022, ATLAS also observed X(6900),{{Cite web|title=ATLAS observes potential four-charm tetraquark|url=https://atlas.cern/Updates/Briefing/Charm-Tetraquark|access-date=2022-07-21|publisher=ATLAS|date=9 July 2022}} and in 2023, CMS reported an observation of three such states, X(6600), X(6900), and X(7300).{{cite web | title = CMS Observes A Potential Family Of Tetra-Quark States Composed Only Of Charm Quarks | url = https://cms.cern/news/cms-observes-potential-family-tetra-quark-states-composed-only-charm-quarks | date = 22 March 2023 | access-date = 22 July 2024 | publisher = CMS}}
In 2021, LHCb announced the discovery of four additional tetraquarks, including c{{overline|c}}u{{overline|s}}.{{cite journal|last1=LHCb collaboration|last2=Aaij|first2=R.|last3=Beteta|first3=C. Abellán|last4=Ackernley|first4=T.|last5=Adeva|first5=B.|last6=Adinolfi|first6=M.|last7=Afsharnia|first7=H.|last8=Aidala|first8=C. A.|last9=Aiola|first9=S.|last10=Ajaltouni|first10=Z.|last11=Akar|first11=S.|date=2021-03-02|title=Observation of New Resonances Decaying to J/ψK+ and J/ψϕ|journal=Physical Review Letters|volume=127|issue=8|page=082001|doi=10.1103/PhysRevLett.127.082001|pmid=34477418|arxiv=2103.01803|bibcode=2021PhRvL.127h2001A|s2cid=232092368}}
In 2022, LHCb announced the discovery of c{{overline|s}}u{{overline|d}} and c{{overline|s}}{{overline|u}}d.{{cite web|url=https://home.cern/news/news/physics/lhcb-discovers-three-new-exotic-particles|title=LHCb discovers three new exotic particles|work=CERN|date=5 July 2022|accessdate=8 July 2022}}
{{Clear}}
See also
References
{{Reflist}}
External links
- [http://belle.kek.jp The Belle experiment] ([https://web.archive.org/web/20040401115040/http://www.kek.jp/press/2003/belle4e.html press release])
- {{cite web|title=LHCb confirms existence of exotic hadrons|url=http://home.web.cern.ch/about/updates/2014/04/lhcb-confirms-existence-exotic-hadrons|first=Cian|last=O'Luanaigh|work=cern.ch|publisher=CERN|location=Geneva, Switzerland|access-date=2014-04-12}}
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