Editing Gluon

{{short description|Elementary particle that mediates the strong force}}

<!-- infobox -->
{{Infobox Particle
| bgcolour        =
| name            = Gluon
| image           = [[File:Feynmann Diagram Gluon Radiation.svg|200px|class=skin-invert-image]]
| caption         = Diagram 1: In [[Feynman diagram]]s, emitted gluons are represented as helices.                                 This diagram depicts the [[Electron–positron annihilation|annihilation of an electron and positron]].
| num_types       = 8<ref>{{cite web | url=https://math.ucr.edu/home/baez/physics/ParticleAndNuclear/gluons.html | title=Why are there eight gluons? }}</ref>
| composition     = [[Elementary particle]]
| statistics      = [[Bosonic]]
| group           = [[Gauge boson]]
| generation      =
| interaction     = [[Strong interaction]]
| theorized       = [[Murray Gell-Mann]] (1962)<ref>
 {{cite journal
  |author=M. Gell-Mann
  |year=1962
  |title=Symmetries of Baryons and Mesons
  |journal=[[Physical Review]]
  |volume=125 |issue=3 |pages=1067–1084
  |doi=10.1103/PhysRev.125.1067
  |bibcode=1962PhRv..125.1067G
  |url=https://authors.library.caltech.edu/4650/1/GELpr63.pdf |archive-url=https://web.archive.org/web/20121021162221/http://authors.library.caltech.edu/4650/1/GELpr63.pdf |archive-date=2012-10-21 |url-status=live
  |doi-access=free
 }}. This is without reference to color, however.  For the modern usage see {{cite journal |last1=Fritzsch |first1=H. |last2=Gell-Mann |first2=M. |last3=Leutwyler |first3=H. |title=Advantages of the color octet gluon picture |journal=Physics Letters B |date=Nov 1973 |volume=47 |issue=4 |pages=365–368 |doi=10.1016/0370-2693(73)90625-4|bibcode=1973PhLB...47..365F |citeseerx=10.1.1.453.4712 }}</ref>
| discovered      =
e<sup>+</sup>e<sup>−</sup> &rarr; Υ(9.46) &rarr; 3g: 1978 at [[DESY#DORIS|DORIS]] ([[DESY]]) by [[PLUTO experiments]] (see diagram 2 and recollection<ref name="SMY">
 {{cite journal
  |author=B.R. Stella and H.-J. Meyer
  |year=2011
  |title=Υ(9.46 GeV) and the gluon discovery (a critical recollection of PLUTO results)
  |journal=[[European Physical Journal H]]
  |volume=36 |issue=2 |pages=203–243
  |arxiv=1008.1869v3
  |bibcode=2011EPJH...36..203S
  |doi=10.1140/epjh/e2011-10029-3
  |s2cid=119246507
 }}</ref>)<br /> 
and <br />
e<sup>+</sup>e<sup>−</sup> &rarr; q{{overline|q}}g: 1979 at [[PETRA]] ([[DESY]]) by [[TASSO]], [[MARK-J]], [[JADE particle detector|JADE]] and [[PLUTO detector|PLUTO experiment]]s (see diagram 1 and review<ref name="SOE">
 {{cite journal
  |author=P. Söding
  |year=2010
  |title=On the discovery of the gluon
  |journal=[[European Physical Journal H]]
  |volume=35 |issue=1 |pages=3–28
  |bibcode=2010EPJH...35....3S
  |doi=10.1140/epjh/e2010-00002-5
  |s2cid=8289475
  |url=http://bib-pubdb1.desy.de/record/92607
 }}</ref>)
| symbol          = g
| mass            = {{nowrap|0 (theoretical value)}}<ref name="pdg"/>{{br}}{{nowrap|&lt; {{val|1.3|u=MeV/''c''<sup>2</sup>}} (experimental limit)}} <ref>
 {{cite journal
  |author=F. Yndurain
  |year=1995
  |title=Limits on the mass of the gluon
  |journal=[[Physics Letters B]]
  |volume=345 |issue=4 |page=524
  |bibcode=1995PhLB..345..524Y
  |doi=10.1016/0370-2693(94)01677-5
 }}</ref><ref name="pdg"/>
| decay_time      = 
| decay_particle  = 
| electric_charge = 0&nbsp;[[elementary charge|''e'']]{{px2}}<ref name="pdg">
 {{cite journal
  |author=W.-M. Yao
  |display-authors=etal
  |collaboration=[[Particle Data Group]]
  |year=2006
  |title=Review of Particle Physics
  |journal=[[Journal of Physics G]]
  |volume=33 |issue=1
  |page=1
  |bibcode=2006JPhG...33....1Y
  |doi=10.1088/0954-3899/33/1/001
  |doi-access=free
  |arxiv=astro-ph/0601168
  }}</ref>
| color_charge    = octet (8 [[linear independence|linearly independent]] types)
| spin            = 1&nbsp;[[reduced Planck constant|''ħ'']]
| num_spin_states = 
| parity          = −1
}}
{{Standard model of particle physics}}

<!-- Lead start -->
A '''gluon''' ({{IPAc-en|ˈ|ɡ|l|uː|ɒ|n}} {{Respell|GLOO|on}}) is a type of [[Massless particle|massless]] [[elementary particle]] that mediates the [[strong interaction]] between [[quark]]s, acting as the [[exchange particle]] for the interaction. Gluons are massless [[vector boson]]s, thereby having a [[Spin (physics)|spin]] of 1.<ref>{{cite web |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/expar.html |title=Gluons |website=hyperphysics.phy-astr.gsu.edu |access-date=2023-09-02}}</ref> Through the strong interaction, gluons bind quarks into groups according to [[quantum chromodynamics|quantum chromodynamics (QCD)]], forming [[hadron]]s such as [[proton]]s and [[neutron]]s.

Gluons carry the [[color charge]] of the strong interaction, thereby participating in the strong interaction as well as mediating it. Because gluons carry the color charge, QCD is more difficult to analyze compared to [[quantum electrodynamics|quantum electrodynamics (QED)]] where the [[photon]] carries no electric charge.

The term was coined by [[Murray Gell-Mann]] in 1962{{Efn|In an interview, Gell-Mann said that he believes the term was coined by [[Edward Teller]].<ref>{{Cite interview |last=Gell-Mann |first=Murray |interviewer=Geoffrey West |title=Feynman's parton |url=https://www.webofstories.com/play/murray.gell-mann/131 |issue=131 |date=1997}}</ref>}} for being similar to an [[adhesive]] or glue that keeps the nucleus together.<ref>{{Cite web |last=Garisto |first=Daniel |date=2017-05-30 |title=A brief etymology of particle physics {{!}} symmetry magazine |url=https://www.symmetrymagazine.org/article/brief-etymology-particle-physics?language_content_entity=und |access-date=2024-02-02 |website=Symmetry Magazine |language=en}}</ref> Together with the quarks, these particles were referred to as [[Parton (particle physics)|partons]] by [[Richard Feynman]].<ref>{{Cite journal |last=Feltesse |first=Joël |date=2010 |title=Introduction to Parton Distribution Functions |journal=Scholarpedia |language=en |volume=5 |issue=11 |pages=10160 |doi=10.4249/scholarpedia.10160 |doi-access=free |bibcode=2010SchpJ...510160F |issn=1941-6016}}</ref>

== Properties ==
The gluon is a [[vector boson]], which means it has a [[Spin (physics)|spin]] of 1&nbsp;''ħ''. While massive spin-1 particles have three polarization states, [[Massless particle|massless]] gauge bosons like the gluon have only two polarization states because [[gauge invariance]] requires the field polarization to be transverse to the direction that the gluon is traveling. In [[quantum field theory]], unbroken gauge invariance requires that gauge bosons have zero mass.  Experiments limit the gluon's rest mass (if any) to less than a few MeV/''c''<sup>2</sup>. The gluon has negative intrinsic [[parity (physics)|parity]].

== Counting gluons ==
There are eight independent types of gluons in QCD. This is unlike the photon of QED or the three [[W and Z bosons]] of the [[weak interaction]]. 

Additionally, gluons are subject to the [[color charge]] phenomena. [[Quark]]s carry three types of color charge; antiquarks carry three types of anticolor. Gluons carry both color and anticolor. This gives nine ''possible'' combinations of color and anticolor in gluons. The following is a list of those combinations (and their schematic names):
* red–antired (''r''{{overline|''r''}}), red–antigreen (''r''{{overline|''g''}}), red–antiblue (''r''{{overline|''b''}})
* green–antired (''g''{{overline|''r''}}), green–antigreen (''g''{{overline|''g''}}), green–antiblue (''g''{{overline|''b''}})
* blue–antired (''b''{{overline|''r''}}), blue–antigreen (''b''{{overline|''g''}}), blue–antiblue (''b''{{overline|''b''}})

[[File:Feynman Diagram Y-3g.svg|thumb|240px|right|class=skin-invert-image|Diagram 2: e<sup>+</sup>e<sup>−</sup> &rarr; Υ(9.46) &rarr; 3g]]
These ''possible'' combinations are only ''effective'' states, not the ''actual'' observed color states of gluons. To understand how they are combined, it is necessary to consider the mathematics of color charge in more detail.

=== Color singlet states <span class="anchor" id="Color singlet"></span> ===
The stable strongly interacting particles, including hadrons like the proton or the neutron, are observed to be "colorless". More precisely, they are in a "color singlet" state, and mathematically analogous to a [[singlet state|''spin'' singlet state]].<ref name="Griff">
{{cite book
 |author=David Griffiths
 |year=1987
 |title=Introduction to Elementary Particles
 |pages=280–281
 |publisher=[[John Wiley & Sons]]
 |isbn=978-0-471-60386-3
}}</ref> The states allow interaction with other color singlets, but not other color states; because long-range gluon interactions do not exist, this illustrates that gluons in the singlet state do not exist either.<ref name="Griff"/>

The color singlet state is:<ref name="Griff"/>
: <math>(r\bar{r}+b\bar{b}+g\bar{g})/\sqrt{3}.</math>

If one could [[Measurement in quantum mechanics|measure]] the color of the state, there would be equal probabilities of it being red–antired, blue–antiblue, or green–antigreen.

=== Eight color states ===
<!-- the link "eight gluon types" from the article "Quark" links here -->
There are eight remaining independent color states corresponding to the "eight types" or "eight colors" of gluons. Since the states can be mixed together, there are multiple ways of presenting these states. These are known as the "color octet", and a commonly used list for each is:<ref name="Griff"/>

: {|
|-
|<math>(r\bar{b}+b\bar{r})/\sqrt{2}</math>
|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
|<math>-i(r\bar{b}-b\bar{r})/\sqrt{2}</math>
|-
|<math>(r\bar{g}+g\bar{r})/\sqrt{2}</math>
|
|<math>-i(r\bar{g}-g\bar{r})/\sqrt{2}</math>
|-
|<math>(b\bar{g}+g\bar{b})/\sqrt{2}</math>
|
|<math>-i(b\bar{g}-g\bar{b})/\sqrt{2}</math>
|-
|<math>(r\bar{r}-b\bar{b})/\sqrt{2}</math>
|
|<math>(r\bar{r}+b\bar{b}-2g\bar{g})/\sqrt{6}</math>
|}

These are equivalent to the [[Gell-Mann matrices]]. The critical feature of these particular eight states is that they are [[linearly independent]], and also independent of the singlet state, hence 3<sup>2</sup>&nbsp;&minus;&nbsp;1 or 2<sup>3</sup>. There is no way to add any combination of these states to produce any others. It is also impossible to add them to make ''r''{{overline|''r''}}, ''g''{{overline|''g''}}, or ''b''{{overline|''b''}}<ref>{{cite web  |author=J. Baez |title=Why are there eight gluons and not nine?  |url=http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/gluons.html |website=math.ucr.edu  |access-date=2009-09-13}}</ref> the forbidden [[singlet state]]. There are many other possible choices, but all are mathematically equivalent, at least equally complicated, and give the same physical results.

=== Group theory details ===
Formally, QCD is a [[gauge theory]] with [[SU(3)]] gauge symmetry. Quarks are introduced as [[spinor]]s in ''N''<sub>f</sub> [[flavour (particle physics)|flavor]]s, each in the [[fundamental representation]] (triplet, denoted '''3''') of the color gauge group, SU(3). The gluons are vectors in the [[Adjoint representation of a Lie group|adjoint representation]] (octets, denoted '''8''') of color SU(3). For a general [[lie group|gauge group]], the number of force-carriers, like photons or gluons, is always equal to the dimension of the adjoint representation. For the simple case of SU(''n''), the dimension of this representation is {{nowrap|{{itco|''n''}}<sup>2</sup> − 1}}.

In group theory, there are no color singlet gluons because [[quantum chromodynamics]] has an SU(3) rather than a [[U(N)|U(3)]] symmetry. There is no known [[A priori and a posteriori|''a priori'']] reason for one group to be preferred over the other, but as discussed above, the experimental evidence supports SU(3).<ref name="Griff"/> If the group were U(3), the ninth (colorless singlet) gluon would behave like a "second photon" and not like the other eight gluons.<ref>{{cite web |url=https://www.forbes.com/sites/startswithabang/2020/11/18/why-are-there-only-8-gluons/|title=Why Are There Only 8 Gluons?|website=[[Forbes]]}}</ref>

== Confinement ==
{{main|Color confinement}}
Since gluons themselves carry color charge, they participate in strong interactions. These gluon–gluon interactions constrain color fields to string-like objects called "[[QCD string|flux tube]]s", which exert constant force when stretched. Due to this force, [[quark]]s are [[color confinement|confined]] within [[composite particle]]s called [[hadron]]s. This effectively limits the range of the strong interaction to {{val|e=-15|u=m}}, roughly the size of a [[nucleon]]. Beyond a certain distance, the energy of the flux tube binding two quarks increases linearly. At a large enough distance, it becomes energetically more favorable to pull a quark–antiquark pair out of the vacuum rather than increase the length of the flux tube.

One consequence of the hadron-confinement property of gluons is that they are not directly involved in the [[nuclear force]]s between hadrons. The force mediators for these are other hadrons called [[meson]]s.

Although in the [[normal phase of QCD]] single gluons may not travel freely, it is predicted that there exist hadrons that are formed entirely of gluons — called [[glueball]]s. There are also conjectures about other [[exotic hadron]]s in which real gluons (as opposed to [[virtual particle|virtual]] ones found in ordinary hadrons) would be primary constituents. Beyond the normal phase of QCD (at extreme temperatures and pressures), [[quark–gluon plasma]] forms. In such a plasma there are no hadrons; quarks and gluons become free particles.

== Experimental observations ==
[[Quark]]s and gluons (colored) manifest themselves by fragmenting into more quarks and gluons, which in turn hadronize into normal (colorless) particles, correlated in jets. As revealed in 1978&nbsp;summer conferences,<ref name="SMY"/> the [[PLUTO detector]] at the electron-positron collider DORIS ([[DESY]]) produced the first evidence that the hadronic decays of the very narrow resonance Υ(9.46) could be interpreted as [[three-jet event]] topologies produced by three gluons. Later, published analyses by the same experiment confirmed this interpretation and also the spin&nbsp;=&nbsp;1 nature of the gluon<ref>{{cite journal |author1=Berger, Ch. |display-authors=etal |collaboration=PLUTO collaboration |year=1979 |title=Jet analysis of the Υ(9.46) decay into charged hadrons |journal=[[Physics Letters B]] |volume=82 |page=449 |bibcode=1979PhLB...82..449B |doi=10.1016/0370-2693(79)90265-X |issue=3–4 |df=dmy-all}}</ref><ref>{{cite journal |author=Berger, Ch. |display-authors=etal |collaboration=PLUTO collaboration |year=1981 |title=Topology of the Υ decay |journal=[[Zeitschrift für Physik C]] |volume=8 |page=101 |bibcode=1981ZPhyC...8..101B |doi=10.1007/BF01547873 |issue=2 |s2cid=124931350 |df=dmy-all}}</ref> (see also the recollection<ref name="SMY"/> and [[PLUTO experiments]]).

In summer&nbsp;1979, at higher energies at the electron-positron collider [[PETRA]] (DESY), again three-jet topologies were observed, now clearly visible and interpreted as q{{overline|q}} gluon [[bremsstrahlung]], by [[TASSO]],<ref>{{cite journal |author=Brandelik, R. |display-authors=etal |collaboration=[[TASSO collaboration]] |year=1979 |title=Evidence for Planar Events in e<sup>+</sup>e<sup>−</sup> annihilation at High Energies |journal=[[Physics Letters B]] |volume=86 |issue=2 |pages=243–249 |bibcode=1979PhLB...86..243B |doi=10.1016/0370-2693(79)90830-X}}</ref> [[MARK-J]]<ref>{{cite journal |author1=Barber, D.P. |s2cid=13903005 |display-authors=etal |collaboration=MARK-J collaboration |year=1979 |title=Discovery of Three-Jet Events and a Test of Quantum Chromodynamics at PETRA |journal=[[Physical Review Letters]] |volume=43 |page=830 |bibcode=1979PhRvL..43..830B |doi= 10.1103/PhysRevLett.43.830 |issue=12 |df=dmy-all}}</ref> and PLUTO experiments<ref>{{cite journal |author=Berger, Ch. |display-authors=etal |collaboration=PLUTO collaboration |year=1979 |title=Evidence for Gluon Bremsstrahlung in e<sup>+</sup>e<sup>−</sup> Annihilations at High Energies |journal=[[Physics Letters B]] |volume=86 |page=418 |bibcode=1979PhLB...86..418B |doi=10.1016/0370-2693(79)90869-4 |issue=3–4 |df=dmy-all}}</ref> (later in 1980 also by [[JADE (particle detector)|JADE]]<ref>{{cite journal |author1=Bartel, W. |display-authors=etal |collaboration=JADE collaboration |year=1980 |title=Observation of planar three-jet events in e<sup>+&nbsp;</sup>e<sup>&minus;</sup> annihilation and evidence for gluon bremsstrahlung |journal=[[Physics Letters B]] |volume=91 |issue=1 |page=142 |bibcode=1980PhLB...91..142B |doi=10.1016/0370-2693(80)90680-2 |url=http://bib-pubdb1.desy.de/search?p=id:%22PUBDB-2017-02984%22 |df=dmy-all}}</ref>). The spin&nbsp;=&nbsp;1 property of the gluon was confirmed in 1980 by TASSO<ref>{{cite journal |author1=Brandelik, R. |display-authors=etal |collaboration=[[TASSO collaboration]] |year=1980 |title=Evidence for a spin-1 gluon in three-jet events |journal=[[Physics Letters B]] |volume=97 |issue=3–4 |page=453 |bibcode=1980PhLB...97..453B |doi=10.1016/0370-2693(80)90639-5 |df=dmy-all}}</ref> and PLUTO experiments<ref>{{cite journal |author1=Berger, Ch. |display-authors=etal |collaboration=PLUTO collaboration |year=1980 |title=A study of multi-jet events in e<sup>+&nbsp;</sup>e<sup>&minus;</sup> annihilation |journal=[[Physics Letters B]] |volume=97 |issue=3–4 |page=459 |bibcode=1980PhLB...97..459B |doi=10.1016/0370-2693(80)90640-1 |df=dmy-all}}</ref> (see also the review<ref name="SOE"/>). In 1991 a subsequent experiment at the [[LEP]] storage ring at [[CERN]] again confirmed this result.<ref>{{cite journal |author1=Alexander, G. |display-authors=etal |collaboration=[[OPAL detector|OPAL collaboration]] |year=1991 |title=Measurement of three-jet distributions sensitive to the gluon spin in e<sup>+&nbsp;</sup>e<sup>&minus;</sup> Annihilations at √s = 91&nbsp;GeV |journal=[[Zeitschrift für Physik C]] |volume=52 |issue=4 |page=543 |bibcode=1991ZPhyC..52..543A |doi=10.1007/BF01562326 |s2cid=51746005 |url=https://repository.ubn.ru.nl//bitstream/handle/2066/124457/124457.pdf |df=dmy-all}}</ref>

The gluons play an important role in the elementary strong interactions between [[quark]]s and gluons, described by QCD and studied particularly at the electron-proton collider [[HERA]] at DESY. The number and momentum distribution of the gluons in the [[proton]] (gluon density) have been measured by two experiments, [[H1 (particle detector)|H1]] and [[ZEUS]],<ref>{{cite journal |author=Lindeman, L. |collaboration=H1 and ZEUS collaborations |year=1997 |title=Proton structure functions and gluon density at HERA |journal=[[Nuclear Physics B: Proceedings Supplements]] |volume=64 |issue=1 |pages=179–183 |bibcode=1998NuPhS..64..179L |doi=10.1016/S0920-5632(97)01057-8 |df=dmy-all}}</ref> in the years 1996–2007. The gluon contribution to the proton spin has been studied by the [[HERMES experiment]] at HERA.<ref>{{cite web |url=http://www-hermes.desy.de |title=The spinning world at DESY |website=www-hermes.desy.de |access-date=26 March 2018 |df=dmy-all |archive-date=25 May 2021 |archive-url=https://web.archive.org/web/20210525042229/http://www-hermes.desy.de/ |url-status=dead }}</ref> The gluon density in the proton (when behaving hadronically) also has been measured.<ref>{{cite journal |author1=Adloff, C. |display-authors=etal |collaboration=H1 collaboration |year=1999 |title=Charged particle cross sections in the photoproduction and extraction of the gluon density in the photon |journal=[[European Physical Journal C]] |volume=10 |issue=3 |pages=363–372 |arxiv=hep-ex/9810020 |bibcode=1999EPJC...10..363H |doi=10.1007/s100520050761 |s2cid=17420774 |df=dmy-all}}</ref>

[[Color confinement]] is verified by the failure of [[free quark]] searches (searches of fractional charges). Quarks are normally produced in pairs (quark + antiquark) to compensate the quantum color and flavor numbers; however at [[Fermilab]] single production of [[top quark]]s has been shown.{{efn|Technically the single [[top quark]]  production at [[Fermilab]] still involves a pair production, but the quark and antiquark are of different flavors.}}<ref>{{cite web |author=Chalmers, M. |date=6 March 2009 |title=Top result for Tevatron |url=https://physicsworld.com/a/top-result-for-tevatron/ <!-- dead link http://physicsworld.com/cws/article/news/38140 --> |work=[[Physics World]] |access-date=2012-04-02 |df=dmy-all}}</ref> No [[glueball]] has been demonstrated.

[[Deconfinement]] was claimed in 2000 at CERN SPS<ref>{{cite journal |author1=Abreu, M.C. |display-authors=etal |collaboration=NA50 collaboration |year=2000 |title=Evidence for deconfinement of quark and antiquark from the J/Ψ suppression pattern measured in Pb-Pb collisions at the CERN SpS |journal=[[Physics Letters B]] |volume=477 |issue=1–3 |pages=28–36 |bibcode=2000PhLB..477...28A  |doi=10.1016/S0370-2693(00)00237-9 |df=dmy-all|url=https://cds.cern.ch/record/427590 }}</ref> in [[heavy-ion collisions]], and it implies a new state of matter: [[quark–gluon plasma]], less interactive than in the [[Atomic nucleus|nucleus]], almost as in a liquid. It was found at the [[Relativistic Heavy Ion Collider]] (RHIC) at Brookhaven in the years 2004–2010 by four contemporaneous experiments.<ref>{{cite news |author=Overbye, D. |date=15 February 2010 |title=In Brookhaven collider, scientists briefly break a law of nature |url=https://www.nytimes.com/2010/02/16/science/16quark.html |archive-url=https://ghostarchive.org/archive/20220102/https://www.nytimes.com/2010/02/16/science/16quark.html |archive-date=2022-01-02 |url-access=limited |url-status=live |work=[[The New York Times]] |access-date=2012-04-02 |df=dmy-all}}{{cbignore}}</ref> A quark–gluon plasma state has been confirmed at the [[CERN]] Large Hadron Collider (LHC) by the three experiments [[A Large Ion Collider Experiment|ALICE]], [[ATLAS experiment|ATLAS]] and [[Compact Muon Solenoid|CMS]] in 2010.<ref>{{cite press release |date=26 November 2010 |title=LHC experiments bring new insight into primordial universe |url=http://press.cern/press-releases/2010/11/lhc-experiments-bring-new-insight-primordial-universe |publisher=[[CERN]] |access-date=2016-11-20 |df=dmy-all}}</ref>

[[Jefferson Lab]]'s [[Continuous Electron Beam Accelerator Facility]], in [[Newport News, Virginia]],{{efn|[[Jefferson Lab]] is a [[nickname]] for the [[Thomas Jefferson National Accelerator Facility]] in [[Newport News, Virginia]].}} is one of 10&nbsp;[[United States Department of Energy|Department of Energy]] facilities doing research on gluons. The Virginia lab was competing with another facility – [[Brookhaven National Laboratory]], on Long Island, New York – for funds to build a new [[electron-ion collider]].<ref>{{cite news |last1=Nolan |first1=Jim |title=State hopes for big economic bang as Jeff Lab bids for ion collider |url=http://www.richmond.com/news/virginia/government-politics/article_fc5216f3-13e8-5ebe-85a6-64e054358389.html |access-date=19 October 2015 |newspaper=Richmond Times-Dispatch |date=October 19, 2015 |pages=A1, A7 |quote=Those clues can give scientists a better understanding of what holds the universe together. |df=dmy-all}}</ref> In December 2019, the US Department of Energy selected the [[Brookhaven National Laboratory]] to host the [[electron-ion collider]].<ref>{{cite press release |date=9 January 2020 |title=U.S. Department of Energy selects Brookhaven National Laboratory to host major new nuclear physics facility |url=https://www.energy.gov/articles/us-department-energy-selects-brookhaven-national-laboratory-host-major-new-nuclear-physics |publisher=[[United States Department of Energy|DOE]] |access-date=2020-06-01 |df=dmy-all}}</ref>

== See also ==
{{div col|colwidth=18em}}
* [[Quark]]
* [[Hadron]]
* [[Meson]]
* [[Gauge boson]]
* [[Quark model]]
* [[Quantum chromodynamics]]
* [[Quark–gluon plasma]]
* [[Color confinement]]
* [[Glueball]]
* [[Gluon field]]
* [[Gluon field strength tensor]]
* [[Exotic hadron]]s
* [[Standard Model]]
* [[Three-jet event]]
* [[Deep inelastic scattering]]
* [[Quantum chromodynamics binding energy]]
* [[Special unitary group]]
* [[Hadronization]]
* [[Color charge]]
* [[Coupling constant]]
{{div col end}}

== Footnotes ==
{{notelist}}

== References ==
{{reflist|25em}}

== Further reading ==
{{commons category|Gluons}}
* {{cite journal
 |author=A. Ali and G. Kramer
 |year=2011
 |title=JETS and QCD: A historical review of the discovery of the quark and gluon jets and its impact on QCD
 |journal=[[European Physical Journal H]]
 |volume=36 |issue=2 |pages=245–326
 |arxiv=1012.2288
 |bibcode = 2011EPJH...36..245A
 |doi=10.1140/epjh/e2011-10047-1
 |s2cid=54062126
}}

* [https://www.hep.phy.cam.ac.uk/~thomson/lectures/partIIIparticles/Handout8_2009.pdf Cambridge Handout 8 : Quantum Chromodynamics – Particle Physics]

== External resources ==
* [https://bigthink.com/starts-with-a-bang/why-are-there-only-8-gluons/ Big Think website, clear explanation of the QCD Octet]
* [https://math.ucr.edu/home/baez/physics/ParticleAndNuclear/gluons.html#:~:text=So%2C%20there%20can%20only%20be,states%20of%20the%20Lie%20algebra. Why are there eight gluons and not nine?]

{{Particles}}

{{Authority control}}

[[Category:Bosons]]
[[Category:Elementary particles]]
[[Category:Gauge bosons]]
[[Category:Gluons]]
[[Category:Quantum chromodynamics]]
[[Category:Force carriers]]
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