Tetraquark
Template: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,<ref>Template:Cite journal</ref> 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.<ref name=":0" /><ref name=":1" />
History and discoveriesEdit
Template:Create list Several tetraquark candidates have been reported by particle physics experiments in the 21st century. The quark contents of these states are almost all qTemplate:OverlineQTemplate:Overline, 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 qqTemplate:OverlineTemplate:Overline (or Template:OverlineTemplate:OverlineQQ) have been discussed by theoretical physicists for a long time, however these are yet to be reported by experiments.<ref>Template:Cite journal</ref>
- Timeline
In 2003, a particle temporarily called X(3872), by the Belle experiment in Japan, was proposed to be a tetraquark candidate,<ref> {{#invoke:citation/CS1|citation |CitationClass=web }}</ref> as originally theorized.<ref> Template:Cite journal</ref> 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 Template:Val.
In 2004, the DsJ(2632) state seen in Fermilab's SELEX was suggested as a possible tetraquark candidate.<ref>Template:Cite journal</ref>
In 2007, Belle announced the observation of the Z(4430) state, a Template:Subatomic particleTemplate:Subatomic particleTemplate:Subatomic particleTemplate:Subatomic particle tetraquark candidate. There are also indications that the Y(4660), also discovered by Belle in 2007, could be a tetraquark state.<ref> Template:Cite journal</ref>
In 2009, Fermilab announced that they have discovered a particle temporarily called Y(4140), which may also be a tetraquark.<ref name="monkeywrench"> {{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
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|Template:SubatomicParticle(5S) meson]] (a form of bottomonium), a well-defined tetraquark resonance exists.<ref name="physicsworld">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref> Template:Cite journal</ref>
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.<ref> Template:Cite journal</ref>
In 2014, the Large Hadron Collider experiment LHCb confirmed the existence of the Z(4430) state with a significance of over 13.9 σ.<ref> {{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="LHCb"> Template:Cite journal</ref>
In February 2016, the DØ experiment reported evidence of a narrow tetraquark candidate, named X(5568), decaying to Template:Subatomic particleTemplate:SubatomicParticle.<ref> Template:Cite journal</ref> In December 2017, DØ also reported observing the X(5568) using a different Template:Subatomic particle final state.<ref>Template:Cite journal</ref> However, it was not observed in searches by the LHCb,<ref> {{#invoke:citation/CS1|citation |CitationClass=web }}</ref> CMS,<ref>Template:Cite journal</ref> CDF,<ref>Template:Cite journal</ref> or ATLAS<ref>Template:Cite journal</ref> experiments.
In June 2016, LHCb announced the discovery of three additional tetraquark candidates, called X(4274), X(4500) and X(4700).<ref>Announcement by LHCb</ref><ref> Template:Cite journal</ref><ref> Template:Cite journal</ref>
In 2020, LHCb announced the discovery of a Template:Subatomic particleTemplate:Subatomic particleTemplate:Subatomic particleTemplate:Subatomic particle tetraquark: X(6900).<ref name=":0"> Template:Cite journal</ref><ref> {{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In 2022, ATLAS also observed X(6900),<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and in 2023, CMS reported an observation of three such states, X(6600), X(6900), and X(7300).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
In 2021, LHCb announced the discovery of four additional tetraquarks, including cTemplate:OverlineuTemplate:Overline.<ref name=":1">Template:Cite journal</ref>
In 2022, LHCb announced the discovery of cTemplate:OverlineuTemplate:Overline and cTemplate:OverlineTemplate:Overlined.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
See alsoEdit
ReferencesEdit
External linksEdit
- The Belle experiment (press release)
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