Latest revision as of 22:05, 20 May 2026

← Back to Plasma and fusion physics

Quark–gluon plasma (QGP or quark soup^[1]) is a hot, dense state of matter in which quarks and gluons are no longer confined inside hadrons. In ordinary nuclear matter, quarks are bound inside protons and neutrons by quantum chromodynamics (QCD); in quark–gluon plasma they are deconfined and move collectively in a strongly interacting medium.

Quark–gluon plasma occurs at energy densities high enough to melt the protons and neutrons that make up atomic nuclei. It is a very low-viscosity liquid composed of elementary quarks and gluons, a state of matter new to physics when it was discovered.^[2]^[3]

Quark–gluon plasma is studied to understand the characteristics of the Universe at about 20 μs after the Big Bang. Experimental groups use ultrarelativistic beams of ions colliding with other ions or protons to create this plasma in particle accelerators.^[4]

History

Theories predicting the existence of quark–gluon plasma were developed in the late 1970s and early 1980s.^[5] The discovery of color confinement and asymptotic freedom in QCD led to the realization that quark matter would undergo a phase transition at high temperature or density.^[6] Using an analogy with electromagnetic plasma, E. V. Shuryak used the term "hadronic plasma" in 1978 for matter much denser than atomic nuclei, in which hadrons merge and quarks act collectively.^[7] In his next paper he used "quark-gluon plasma", the name that became standard.^[6]^: 1125^[8]

In 2000, CERN issued a press release^[9] reporting evidence for a new state of matter based on Pb-Pb heavy-ion collision studies.^[10]^[11] The evidence was consistent with many characteristics of the theoretically predicted quark-gluon plasma.^[2]

A competing team at the Relativistic Heavy Ion Collider (RHIC) characterized the CERN results as circumstantial^[12] and suggested that the experiments yielded little information about the properties of the new state.^[13] A series of Au-Au collision studies from RHIC published in 2005 showed that the collisions produce something more like a liquid than the weakly interacting gas expected in early theoretical models.^[14]

Role in the Standard Model

QCD is one part of the modern theory of particle physics called the Standard Model. Other parts of this theory describe electroweak interactions and neutrinos. The theory of electrodynamics has been tested and found correct to a few parts in a billion. The theory of weak interactions has been tested and found correct to a few parts in a thousand. Perturbative forms of QCD have been tested to a few percent.^[15] Perturbative models assume relatively small changes from the ground state, simplifying calculations at the cost of generality. In contrast, non-perturbative QCD is much harder to test directly. The study of QGP, which has both high temperature and high density, is part of the effort to understand QCD beyond perturbation theory.

The study of QGP is also a testing ground for finite-temperature field theory, a branch of theoretical physics that studies particle physics under high-temperature conditions. Such studies are important for understanding the early evolution of the Universe, especially the first hundred microseconds after the Big Bang. They are also relevant to grand unification theories, which seek to unify the fundamental forces of nature except gravity.

Occurrence

The generally accepted model of the formation of the Universe states that it happened as the result of the Big Bang. In this model, in the time interval of 10⁻¹⁰–10⁻⁶ s after the Big Bang, matter existed in the form of a quark–gluon plasma. It is possible to reproduce the density and temperature of matter from that early time in laboratory conditions. The main method is the collision of two heavy atomic nuclei accelerated to energies of more than a hundred GeV. A head-on collision creates a small fireball with a volume approximately equal to that of an atomic nucleus, allowing physicists to model the density and temperature of the early Universe.

Relation to electromagnetic plasma

A plasma is matter in which charges are screened by the presence of other mobile charges. For example, Coulomb's law can be modified by screening to yield a distance-dependent charge, $Q \to Q e^{- r / α}$ , where the charge is reduced exponentially with distance divided by a screening length α. In QGP, the color charge of quarks and gluons is screened. QGP has analogies with an ordinary plasma, but also important differences: color charge is non-abelian, whereas electric charge is abelian. Outside a finite volume of QGP the color-electric field is not screened, so a volume of QGP must still be color-neutral and have integer electric charge.

Because of the extremely high energies involved, quark-antiquark pairs are produced by pair production. A QGP is therefore a roughly equal mixture of quarks and antiquarks of various flavors, with only a slight excess of quarks. This is not a general feature of conventional plasmas, which are often too cool for pair production.

Theory

One consequence of the non-abelian color charge is that the interaction is too strong for perturbative computations in many QGP conditions. The main theoretical tools for exploring QGP include lattice gauge theory.^[16]^[17] The transition temperature, approximately 175 MeV in older estimates, was first predicted by lattice gauge theory. Since then, lattice gauge theory has been used to predict many other properties of this kind of matter. The AdS/CFT correspondence may also provide insights into QGP, and the fluid/gravity correspondence has been used as a theoretical framework for understanding strongly coupled fluids. QGP is believed to be a phase of QCD that can become locally thermalized and therefore suitable for an effective fluid-dynamic description.

Production

Production of QGP in the laboratory is achieved by colliding heavy atomic nuclei, or heavy ions, at relativistic energy. Matter is heated well above the Hagedorn temperature T_H = 150 MeV per particle, corresponding to a temperature exceeding 1.66 trillion K. Lead and gold nuclei have been used in such collisions at the CERN Super Proton Synchrotron and at the Brookhaven Relativistic Heavy Ion Collider, respectively. The nuclei are accelerated to ultrarelativistic speeds, directed toward each other, and create a hot fireball in the rare event of a collision. Hydrodynamic simulations predict that this fireball expands under its own pressure and cools while expanding. Measurements of spherical and elliptic flow test these models.

Diagnostic tools

Quark–gluon plasma is produced in relativistic heavy-ion collisions.^[18]^[19]^[20]^[21]

Important classes of experimental observations include:

Thermal photons and thermal dileptons
Strangeness production
Elliptic flow
Jet quenching
J/ψ melting
Hanbury Brown and Twiss effect and Bose–Einstein correlations
Single-particle spectra

Expected properties

Thermodynamics

The cross-over temperature from the normal hadronic phase to the QGP phase is about 156 MeV.^[22] The phenomena involved correspond to an energy density of a little less than 1 GeV/fm³. For relativistic matter, pressure and temperature are not independent variables, so the equation of state is a relation between energy density and pressure. This has been found through lattice computations and compared with perturbation theory and string-theory-inspired models. Response functions such as the specific heat and quark-number susceptibilities are active topics of calculation.

Flow

The discovery of QGP as an almost perfect liquid was a turning point in high-energy nuclear physics. Experiments at RHIC revealed a substance with extremely low resistance to flow.^[23] Nuclear matter at low temperature is known to behave like a superfluid. When heated, the nuclear fluid evaporates into a dilute gas of nucleons and, on further heating, a gas of baryons and mesons. At the critical temperature, hadrons melt and the gas turns back into a liquid. RHIC experiments showed that this liquid has less resistance to flow than any other substance observed in laboratory experiments at any scale. Detailed measurements indicate that it is a quark–gluon plasma in which quarks, antiquarks and gluons flow collectively.^[24]

Schematic representation of the interaction region formed in the first moments after the collision of high-energy heavy ions.^[25]

In short, QGP flows like a splat of liquid and, because it is not transparent to quarks, it can attenuate jets emitted in collisions. Once formed, a ball of QGP transfers heat internally by radiation. However, unlike ordinary hot objects, there is enough energy available for gluons to collide and produce an excess of strange quarks. If QGP did not exist and the collision produced only a non-equilibrium mixture, the same energy would instead create different distributions of heavier quarks such as charm or bottom quarks.^[25]^[26]

The equation of state is an important input into flow equations. The speed of sound, meaning the speed of QGP-density oscillations, is studied in lattice computations.^[27]^[28]^[29] The mean free path of quarks and gluons has been computed using perturbation theory as well as string-theory methods. Lattice computations of transport coefficients indicate that the mean free time of quarks and gluons in QGP may be comparable to the average interparticle spacing, supporting the interpretation of QGP as a liquid.^[30]^[31] The incorporation of dissipative phenomena into hydrodynamics is another active research area.^[32]^[33]^[34]

Jet quenching effect

Detailed predictions for the production of jets were made in the late 1970s for the CERN Super Proton–Antiproton Synchrotron.^[35]^[36]^[37]^[38] The UA2 experiment observed the first evidence for jet production in hadron collisions in 1981,^[39] shortly after confirmed by UA1.^[40]

The subject was later revived at RHIC. One of the most striking physical effects observed at RHIC energies is jet quenching.^[41]^[42]^[43] At the first stage of interaction between colliding relativistic nuclei, partons of the colliding nuclei give rise to secondary partons with large transverse momentum. Passing through hot, compressed plasma, these partons lose energy. The magnitude of energy loss depends on QGP properties such as temperature and density. Colored quarks and gluons are the elementary objects of the plasma, so parton energy loss in QGP differs from energy loss in a medium made of colorless hadrons. Under RHIC conditions, parton energy losses are estimated as $1 |$ . This conclusion is supported by comparing high-transverse-momentum hadron yields in nucleon-nucleon and nucleus-nucleus collisions at the same energy. The reduced yield in nucleus-nucleus collisions suggests that nuclear collisions cannot be regarded as a simple superposition of nucleon-nucleon collisions. For a short time and small volume, quarks and gluons form an almost ideal liquid whose collective properties affect the motion and energy loss of partons.^[44]

In November 2010, CERN announced the first direct observation of jet quenching based on heavy-ion collisions.^[45]^[46]^[47]^[48]

Direct photons and dileptons

Thermal photons and dileptons are important electromagnetic probes of the QGP formed in relativistic heavy-ion collisions. Unlike hadrons, which predominantly reflect the final stages of the collision, electromagnetic probes are emitted throughout the space–time evolution of the fireball, from the early deconfined phase through the hadronic stage up to kinetic freeze-out, when strong interactions cease. Because photons and leptons interact only electromagnetically, their mean free path is much larger than the size of the collision volume. They can therefore escape the medium with minimal final-state interactions and provide direct information about the temperature and dynamics of the matter created in the collision. Dilepton invariant mass helps separate partonic and hadronic effects, making it useful for studying the average temperature of the plasma and its equilibration time.^[49]

Glasma hypothesis

Since 2008, physicists have discussed a hypothetical precursor state of QGP called the glasma, in which dressed particles are condensed into a glassy or amorphous state below the genuine transition between the confined state and the plasma liquid.^[50] This would be analogous to the formation of metallic glasses, or amorphous alloys, below the onset of the liquid metallic state.

Although the high temperatures and densities predicted to produce QGP have been realized in the laboratory, the resulting matter does not behave as a quasi-ideal state of free quarks and gluons. Instead, it behaves as an almost perfect dense fluid.^[51] The possibility that QGP would not yet be free at accelerator temperatures was predicted in 1984 as a consequence of remnant effects of confinement.^[52]^[53]

Neutron stars

It has been hypothesized that the core of some massive neutron stars may contain deconfined quark matter related to quark–gluon plasma.^[54]

Onset of deconfinement

The central issue in the formation of quark–gluon plasma is the search for the onset of deconfinement. From the beginning of QGP research, the question was whether sufficient energy density could be achieved in nucleus-nucleus collisions. This depends on how much energy each nucleon loses. An influential reaction picture was the scaling solution presented by Bjorken.^[55] This model applies to ultra-high-energy collisions. In experiments at CERN SPS and BNL RHIC, the situation is usually divided into three stages:^[56]

@@ Line 1: / Line 1: @@
-{{Short description|Deconfined state of quarks and gluons in high-energy quantum chromodynamics}}
+{{Quantum article nav|previous=Physics:Quantum Lawson criterion|previous label=Lawson criterion|next=Physics:Quantum molecular structure|next label=Molecular structure}}
+{{Short description|Deconfined state of quarks and gluons in high-energy quantum chromodynamics}}
 {{Quantum matter backlink|Plasma and fusion physics}}
@@ Line 10: / Line 14: @@
 <div style="flex:1; line-height:1.45; color:#006b45; column-count:2; column-gap:32px; column-rule:1px solid #b8d8c8;">
-'''Quark–gluon plasma''' ('''QGP''' or '''quark soup'''<ref>{{Cite journal |last=Heinz |first=Ulrich |date=January 20, 2015 |title=Quark–gluon soup — The perfectly liquid phase of QCD |url=[https://www.worldscientific.com/doi/abs/10.1142/S0217751X15300112](https://www.worldscientific.com/doi/abs/10.1142/S0217751X15300112) |journal=International Journal of Modern Physics A |volume=30 |issue=02 |pages=1530011 |doi=10.1142/S0217751X15300112 |issn=0217-751X}}</ref>) is a hot, dense state of [[Physics:Quantum matter/matter|matter]] in which [[Physics:Quantum quark|quarks]] and [[Physics:Quantum gluon|gluons]] are no longer confined inside [[Physics:Quantum hadron|hadrons]]. In ordinary nuclear matter, quarks are bound inside protons and neutrons by [[Physics:Quantum chromodynamics|quantum chromodynamics]] (QCD); in quark–gluon plasma they are [[Physics:Quantum deconfinement|deconfined]] and move collectively in a strongly interacting medium.
+'''Quark–gluon plasma''' ('''QGP''' or '''quark soup'''<ref>{{Cite journal |last=Heinz |first=Ulrich |date=January 20, 2015 |title=Quark–gluon soup — The perfectly liquid phase of QCD |url=[https://www.worldscientific.com/doi/abs/10.1142/S0217751X15300112](https://www.worldscientific.com/doi/abs/10.1142/S0217751X15300112) |journal=International Journal of Modern Physics A |volume=30 |issue=02 |pages=1530011 |doi=10.1142/S0217751X15300112 |issn=0217-751X}}</ref>) is a hot, dense state of matter in which [[Physics:Quantum quark|quarks]] and [[Physics:Quantum gluon|gluons]] are no longer confined inside [[Physics:Quantum hadron|hadrons]]. In ordinary nuclear matter, quarks are bound inside protons and neutrons by [[Physics:Quantum chromodynamics|quantum chromodynamics]] (QCD); in quark–gluon plasma they are deconfined and move collectively in a strongly interacting medium.
-Quark–gluon plasma occurs at [[Energy density|energy densities]] high enough to melt the [[Physics:Quantum proton|protons]] and [[Physics:Quantum neutron|neutrons]] that make up atomic nuclei. It is a very low-[[viscosity]] liquid composed of elementary quarks and gluons, a state of matter new to physics when it was discovered.<ref name="Rafelski-2015" /><ref>{{Cite journal |last1=Braun-Munzinger |first1=Peter |last2=Stachel |first2=Johanna |date=July 2007 |title=The quest for the quark–gluon plasma |url=[https://www.nature.com/articles/nature06080](https://www.nature.com/articles/nature06080) |journal=Nature |language=en |volume=448 |issue=7151 |pages=302–309 |doi=10.1038/nature06080 |pmid=17637661 |issn=0028-0836|url-access=subscription }}</ref>
+Quark–gluon plasma occurs at energy densities high enough to melt the [[Physics:Quantum proton|protons]] and [[Physics:Quantum neutron|neutrons]] that make up atomic nuclei. It is a very low-viscosity liquid composed of elementary quarks and gluons, a state of matter new to physics when it was discovered.<ref name="Rafelski-2015" /><ref>{{Cite journal |last1=Braun-Munzinger |first1=Peter |last2=Stachel |first2=Johanna |date=July 2007 |title=The quest for the quark–gluon plasma |url=[https://www.nature.com/articles/nature06080](https://www.nature.com/articles/nature06080) |journal=Nature |language=en |volume=448 |issue=7151 |pages=302–309 |doi=10.1038/nature06080 |pmid=17637661 |issn=0028-0836|url-access=subscription }}</ref>
-Quark–gluon plasma is studied to understand the characteristics of the Universe at about 20 μs after the [[Big Bang]]. Experimental groups use [[ultrarelativistic]] beams of ions colliding with other ions or protons to create this plasma in [[particle accelerator]]s.<ref>{{Cite journal |last1=Busza |first1=Wit |last2=Rajagopal |first2=Krishna |last3=Schee |first3=Wilke van der |date=October 19, 2018 |title=Heavy Ion Collisions: The Big Picture and the Big Questions |url=[https://www.annualreviews.org/content/journals/10.1146/annurev-nucl-101917-020852](https://www.annualreviews.org/content/journals/10.1146/annurev-nucl-101917-020852) |journal=Annual Review of Nuclear and Particle Science |language=en |volume=68 |pages=339–376 |doi=10.1146/annurev-nucl-101917-020852 |arxiv=1802.04801 |issn=0163-8998}}</ref>
+Quark–gluon plasma is studied to understand the characteristics of the Universe at about 20 μs after the Big Bang. Experimental groups use ultrarelativistic beams of ions colliding with other ions or protons to create this plasma in particle accelerators.<ref>{{Cite journal |last1=Busza |first1=Wit |last2=Rajagopal |first2=Krishna |last3=Schee |first3=Wilke van der |date=October 19, 2018 |title=Heavy Ion Collisions: The Big Picture and the Big Questions |url=[https://www.annualreviews.org/content/journals/10.1146/annurev-nucl-101917-020852](https://www.annualreviews.org/content/journals/10.1146/annurev-nucl-101917-020852) |journal=Annual Review of Nuclear and Particle Science |language=en |volume=68 |pages=339–376 |doi=10.1146/annurev-nucl-101917-020852 |arxiv=1802.04801 |issn=0163-8998}}</ref>
 </div>
@@ Line 24: / Line 28: @@
 == History ==
-Theories predicting the existence of quark–gluon plasma were developed in the late 1970s and early 1980s.<ref>{{Cite book|last=Satz|first=H.|url=[https://books.google.com/books?id=OY8uAAAAIAAJ|title=Statistical](https://books.google.com/books?id=OY8uAAAAIAAJ|title=Statistical) Mechanics of Quarks and Hadrons: Proceedings of an International Symposium Held at the University of Bielefeld, F.R.G., August 24–31, 1980|date=1981|publisher=North-Holland|isbn=978-0-444-86227-3|language=en}}</ref> The discovery of [[Physics:Quantum confinement|color confinement]] and [[Physics:Quantum asymptotic freedom|asymptotic freedom]] in QCD led to the realization that quark matter would undergo a phase transition at high temperature or density.<ref name="Gross-2023"/> Using an analogy with electromagnetic plasma, E. V. Shuryak used the term "hadronic plasma" in 1978 for matter much denser than atomic nuclei, in which hadrons merge and quarks act collectively.<ref>Shuryak, E V. "Theory of hadron plasma." Sov. Phys. - JETP (Engl. Transl.); (United States), vol. 47:2, Jan. 1978.</ref> In his next paper he used "quark-gluon plasma", the name that became standard.<ref name="Gross-2023">{{Cite journal |last1=Gross |first1=Franz |last2=Klempt |first2=Eberhard |last3=Brodsky |first3=Stanley J. |last4=Buras |first4=Andrzej J. |last5=Burkert |first5=Volker D. |last6=Heinrich |first6=Gudrun |last7=Jakobs |first7=Karl |last8=Meyer |first8=Curtis A. |last9=Orginos |first9=Kostas |last10=Strickland |first10=Michael |last11=Stachel |first11=Johanna |last12=Zanderighi |first12=Giulia |last13=Brambilla |first13=Nora |last14=Braun-Munzinger |first14=Peter |last15=Britzger |first15=Daniel |date=December 12, 2023 |title=50 Years of quantum chromodynamics |journal=The European Physical Journal C |language=en |volume=83 |issue=12 |page=1125 |doi=10.1140/epjc/s10052-023-11949-2 |doi-access=free|issn=1434-6052}}</ref>{{rp|1125}}<ref>{{Cite journal |last=Shuryak |first=E. V. |date=September 11, 1978 |title=Quark-gluon plasma and hadronic production of leptons, photons and psions |journal=Physics Letters B |volume=78 |issue=1 |pages=150–153 |doi=10.1016/0370-2693(78)90370-2 |issn=0370-2693}}</ref>
+Theories predicting the existence of quark–gluon plasma were developed in the late 1970s and early 1980s.<ref>{{Cite book|last=Satz|first=H.|url=[https://books.google.com/books?id=OY8uAAAAIAAJ|title=Statistical](https://books.google.com/books?id=OY8uAAAAIAAJ|title=Statistical) Mechanics of Quarks and Hadrons: Proceedings of an International Symposium Held at the University of Bielefeld, F.R.G., August 24–31, 1980|date=1981|publisher=North-Holland|isbn=978-0-444-86227-3|language=en}}</ref> The discovery of color confinement and asymptotic freedom in QCD led to the realization that quark matter would undergo a phase transition at high temperature or density.<ref name="Gross-2023"/> Using an analogy with electromagnetic plasma, E. V. Shuryak used the term "hadronic plasma" in 1978 for matter much denser than atomic nuclei, in which hadrons merge and quarks act collectively.<ref>Shuryak, E V. "Theory of hadron plasma." Sov. Phys. - JETP (Engl. Transl.); (United States), vol. 47:2, Jan. 1978.</ref> In his next paper he used "quark-gluon plasma", the name that became standard.<ref name="Gross-2023">{{Cite journal |last1=Gross |first1=Franz |last2=Klempt |first2=Eberhard |last3=Brodsky |first3=Stanley J. |last4=Buras |first4=Andrzej J. |last5=Burkert |first5=Volker D. |last6=Heinrich |first6=Gudrun |last7=Jakobs |first7=Karl |last8=Meyer |first8=Curtis A. |last9=Orginos |first9=Kostas |last10=Strickland |first10=Michael |last11=Stachel |first11=Johanna |last12=Zanderighi |first12=Giulia |last13=Brambilla |first13=Nora |last14=Braun-Munzinger |first14=Peter |last15=Britzger |first15=Daniel |date=December 12, 2023 |title=50 Years of quantum chromodynamics |journal=The European Physical Journal C |language=en |volume=83 |issue=12 |page=1125 |doi=10.1140/epjc/s10052-023-11949-2 |doi-access=free|issn=1434-6052}}</ref>{{rp|1125}}<ref>{{Cite journal |last=Shuryak |first=E. V. |date=September 11, 1978 |title=Quark-gluon plasma and hadronic production of leptons, photons and psions |journal=Physics Letters B |volume=78 |issue=1 |pages=150–153 |doi=10.1016/0370-2693(78)90370-2 |issn=0370-2693}}</ref>
-In 2000, [[CERN]] issued a press release<ref>{{Cite web|url=[https://home.cern/news/press-release/cern/new-state-matter-created-cern|title=New](https://home.cern/news/press-release/cern/new-state-matter-created-cern|title=New) State of Matter created at CERN|date=10 February 2000|website=CERN|language=en|access-date=2020-03-25}}</ref> reporting evidence for a new state of matter based on Pb-Pb heavy-ion collision studies.<ref>{{cite arXiv|last1=Heinz|first1=Ulrich|last2=Jacob|first2=Maurice|date=2000-02-16|title=Evidence for a New State of Matter: An Assessment of the Results from the CERN Lead Beam Programme|eprint=nucl-th/0002042 }}</ref><ref>{{Cite news|last=Glanz|first=James|date=2000-02-10|title=Particle Physicists Getting Closer To the Bang That Started It All|language=en-US|work=The New York Times|url=[https://www.nytimes.com/2000/02/10/world/particle-physicists-getting-closer-to-the-bang-that-started-it-all.html|access-date=2020-05-10|issn=0362-4331}}](https://www.nytimes.com/2000/02/10/world/particle-physicists-getting-closer-to-the-bang-that-started-it-all.html|access-date=2020-05-10|issn=0362-4331}})</ref> The evidence was consistent with many characteristics of the theoretically predicted quark-gluon plasma.<ref name="Rafelski-2015">{{Cite journal|last=Rafelski|first=Johann|year=2015|title=Melting hadrons, boiling quarks|journal=The European Physical Journal A|language=en|volume=51|issue=9|article-number=114|doi=10.1140/epja/i2015-15114-0|arxiv=1508.03260|s2cid=119191818|issn=1434-6001}}</ref>
+In 2000, CERN issued a press release<ref>{{Cite web|url=[https://home.cern/news/press-release/cern/new-state-matter-created-cern|title=New](https://home.cern/news/press-release/cern/new-state-matter-created-cern|title=New) State of Matter created at CERN|date=10 February 2000|website=CERN|language=en|access-date=2020-03-25}}</ref> reporting evidence for a new state of matter based on Pb-Pb heavy-ion collision studies.<ref>{{cite arXiv|last1=Heinz|first1=Ulrich|last2=Jacob|first2=Maurice|date=2000-02-16|title=Evidence for a New State of Matter: An Assessment of the Results from the CERN Lead Beam Programme|eprint=nucl-th/0002042 }}</ref><ref>{{Cite news|last=Glanz|first=James|date=2000-02-10|title=Particle Physicists Getting Closer To the Bang That Started It All|language=en-US|work=The New York Times|url=[https://www.nytimes.com/2000/02/10/world/particle-physicists-getting-closer-to-the-bang-that-started-it-all.html|access-date=2020-05-10|issn=0362-4331}}](https://www.nytimes.com/2000/02/10/world/particle-physicists-getting-closer-to-the-bang-that-started-it-all.html|access-date=2020-05-10|issn=0362-4331}})</ref> The evidence was consistent with many characteristics of the theoretically predicted quark-gluon plasma.<ref name="Rafelski-2015">{{Cite journal|last=Rafelski|first=Johann|year=2015|title=Melting hadrons, boiling quarks|journal=The European Physical Journal A|language=en|volume=51|issue=9|article-number=114|doi=10.1140/epja/i2015-15114-0|arxiv=1508.03260|s2cid=119191818|issn=1434-6001}}</ref>
-A competing team at the [[Relativistic Heavy Ion Collider]] (RHIC) characterized the CERN results as circumstantial<ref>{{Citation |last1=Collaboration |first1=STAR |title=Experimental and theoretical challenges in the search for the quark–gluon plasma: The STAR Collaboration's critical assessment of the evidence from RHIC collisions |date=2005-04-26 |last2=Adams |first2=J. |journal=Nuclear Physics A |volume=757 |issue=1–2 |pages=102–183 |doi=10.1016/j.nuclphysa.2005.03.085 |arxiv=nucl-ex/0501009 }}</ref> and suggested that the experiments yielded little information about the properties of the new state.<ref>{{Cite journal |last=Stachel |first=Johanna |date=April 10, 2006 |title=Has the quark-gluon plasma been seen? |url=[https://www.worldscientific.com/doi/abs/10.1142/S0217751X06032733](https://www.worldscientific.com/doi/abs/10.1142/S0217751X06032733) |journal=International Journal of Modern Physics A |volume=21 |issue=08n09 |pages=1750–1763 |doi=10.1142/S0217751X06032733 |issn=0217-751X}}</ref> A series of Au-Au collision studies from RHIC published in 2005 showed that the collisions produce something more like a liquid than the weakly interacting gas expected in early theoretical models.<ref>{{Cite web |title=RHIC Scientists Serve Up 'Perfect' Liquid |url=[https://www.bnl.gov/newsroom/news.php?a=110303](https://www.bnl.gov/newsroom/news.php?a=110303) |access-date=2025-11-18 |website=Brookhaven National Laboratory |language=en}}</ref>
+A competing team at the Relativistic Heavy Ion Collider (RHIC) characterized the CERN results as circumstantial<ref>{{Citation |last1=Collaboration |first1=STAR |title=Experimental and theoretical challenges in the search for the quark–gluon plasma: The STAR Collaboration's critical assessment of the evidence from RHIC collisions |date=2005-04-26 |last2=Adams |first2=J. |journal=Nuclear Physics A |volume=757 |issue=1–2 |pages=102–183 |doi=10.1016/j.nuclphysa.2005.03.085 |arxiv=nucl-ex/0501009 }}</ref> and suggested that the experiments yielded little information about the properties of the new state.<ref>{{Cite journal |last=Stachel |first=Johanna |date=April 10, 2006 |title=Has the quark-gluon plasma been seen? |url=[https://www.worldscientific.com/doi/abs/10.1142/S0217751X06032733](https://www.worldscientific.com/doi/abs/10.1142/S0217751X06032733) |journal=International Journal of Modern Physics A |volume=21 |issue=08n09 |pages=1750–1763 |doi=10.1142/S0217751X06032733 |issn=0217-751X}}</ref> A series of Au-Au collision studies from RHIC published in 2005 showed that the collisions produce something more like a liquid than the weakly interacting gas expected in early theoretical models.<ref>{{Cite web |title=RHIC Scientists Serve Up 'Perfect' Liquid |url=[https://www.bnl.gov/newsroom/news.php?a=110303](https://www.bnl.gov/newsroom/news.php?a=110303) |access-date=2025-11-18 |website=Brookhaven National Laboratory |language=en}}</ref>
 == Role in the Standard Model ==
-QCD is one part of the modern theory of [[particle physics]] called the [[Standard Model]]. Other parts of this theory describe [[electroweak interaction]]s and [[neutrino]]s. The theory of electrodynamics has been tested and found correct to a few parts in a billion. The theory of weak interactions has been tested and found correct to a few parts in a thousand. Perturbative forms of QCD have been tested to a few percent.<ref>{{Cite journal|last1=Tanabashi|first1=M.|last2=Hagiwara|first2=K.|last3=Hikasa|first3=K.|last4=Nakamura|first4=K.|last5=Sumino|first5=Y.|last6=Takahashi|first6=F.|last7=Tanaka|first7=J.|last8=Agashe|first8=K.|last9=Aielli|first9=G.|last10=Amsler|first10=C.|last11=Antonelli|first11=M.|year=2018|title=Review of Particle Physics|url=[https://pdg.lbl.gov/2019/reviews/rpp2019-rev-qcd.pdf|journal=Physical](https://pdg.lbl.gov/2019/reviews/rpp2019-rev-qcd.pdf|journal=Physical) Review D|language=en|volume=98|issue=3|pages=1–708|doi=10.1103/PhysRevD.98.030001|pmid=10020536|hdl=11384/78286 |issn=2470-0010}}</ref> Perturbative models assume relatively small changes from the ground state, simplifying calculations at the cost of generality. In contrast, non-perturbative QCD is much harder to test directly. The study of QGP, which has both high temperature and high density, is part of the effort to understand QCD beyond perturbation theory.
+QCD is one part of the modern theory of [[Physics:Quantum particle|particle physics]] called the [[Physics:Quantum Standard Model|Standard Model]]. Other parts of this theory describe electroweak interactions and neutrinos. The theory of electrodynamics has been tested and found correct to a few parts in a billion. The theory of weak interactions has been tested and found correct to a few parts in a thousand. Perturbative forms of QCD have been tested to a few percent.<ref>{{Cite journal|last1=Tanabashi|first1=M.|last2=Hagiwara|first2=K.|last3=Hikasa|first3=K.|last4=Nakamura|first4=K.|last5=Sumino|first5=Y.|last6=Takahashi|first6=F.|last7=Tanaka|first7=J.|last8=Agashe|first8=K.|last9=Aielli|first9=G.|last10=Amsler|first10=C.|last11=Antonelli|first11=M.|year=2018|title=Review of Particle Physics|url=[https://pdg.lbl.gov/2019/reviews/rpp2019-rev-qcd.pdf|journal=Physical](https://pdg.lbl.gov/2019/reviews/rpp2019-rev-qcd.pdf|journal=Physical) Review D|language=en|volume=98|issue=3|pages=1–708|doi=10.1103/PhysRevD.98.030001|pmid=10020536|hdl=11384/78286 |issn=2470-0010}}</ref> Perturbative models assume relatively small changes from the ground state, simplifying calculations at the cost of generality. In contrast, non-perturbative QCD is much harder to test directly. The study of QGP, which has both high temperature and high density, is part of the effort to understand QCD beyond perturbation theory.
-The study of QGP is also a testing ground for [[Thermal quantum field theory|finite-temperature field theory]], a branch of theoretical physics that studies particle physics under high-temperature conditions. Such studies are important for understanding the early evolution of the Universe, especially the first hundred microseconds after the Big Bang. They are also relevant to [[grand unification theory|grand unification theories]], which seek to unify the fundamental forces of nature except gravity.
+The study of QGP is also a testing ground for finite-temperature field theory, a branch of theoretical physics that studies particle physics under high-temperature conditions. Such studies are important for understanding the early evolution of the Universe, especially the first hundred microseconds after the Big Bang. They are also relevant to grand unification theories, which seek to unify the fundamental forces of nature except gravity.
 === Occurrence ===
@@ Line 44: / Line 48: @@
 === Theory ===
-One consequence of the non-abelian color charge is that the interaction is too strong for perturbative computations in many QGP conditions. The main theoretical tools for exploring QGP include [[lattice gauge theory]].<ref>{{Cite journal|last=Karsch|first=F.|year=1995|title=The phase transition to the quark gluon plasma: Recent results from lattice calculations|journal=Nuclear Physics A|language=en|volume=590|issue=1–2|pages=367–381|doi=10.1016/0375-9474(95)00248-Y|arxiv=hep-lat/9503010|s2cid=118967199}}</ref><ref>{{Cite journal |title=The Quark–Gluon Plasma |journal=Nuclear Physics A |volume=862–863 |issue=12 |pages=4–12 |doi=10.1016/j.nuclphysa.2011.05.014|year=2011 |arxiv=1101.3937 |last1=Satz |first1=Helmut |bibcode=2011NuPhA.862....4S |s2cid=118369368 }}</ref> The transition temperature, approximately {{val|175|ul=MeV}} in older estimates, was first predicted by lattice gauge theory. Since then, lattice gauge theory has been used to predict many other properties of this kind of matter. The [[AdS/CFT correspondence]] may also provide insights into QGP, and the fluid/gravity correspondence has been used as a theoretical framework for understanding strongly coupled fluids. QGP is believed to be a phase of QCD that can become locally thermalized and therefore suitable for an effective fluid-dynamic description.
+One consequence of the non-abelian color charge is that the interaction is too strong for perturbative computations in many QGP conditions. The main theoretical tools for exploring QGP include lattice gauge theory.<ref>{{Cite journal|last=Karsch|first=F.|year=1995|title=The phase transition to the quark gluon plasma: Recent results from lattice calculations|journal=Nuclear Physics A|language=en|volume=590|issue=1–2|pages=367–381|doi=10.1016/0375-9474(95)00248-Y|arxiv=hep-lat/9503010|s2cid=118967199}}</ref><ref>{{Cite journal |title=The Quark–Gluon Plasma |journal=Nuclear Physics A |volume=862–863 |issue=12 |pages=4–12 |doi=10.1016/j.nuclphysa.2011.05.014|year=2011 |arxiv=1101.3937 |last1=Satz |first1=Helmut |bibcode=2011NuPhA.862....4S |s2cid=118369368 }}</ref> The transition temperature, approximately {{val|175|ul=MeV}} in older estimates, was first predicted by lattice gauge theory. Since then, lattice gauge theory has been used to predict many other properties of this kind of matter. The AdS/CFT correspondence may also provide insights into QGP, and the fluid/gravity correspondence has been used as a theoretical framework for understanding strongly coupled fluids. QGP is believed to be a phase of QCD that can become locally thermalized and therefore suitable for an effective fluid-dynamic description.
 === Production ===
-Production of QGP in the laboratory is achieved by colliding heavy atomic nuclei, or heavy ions, at relativistic energy. Matter is heated well above the Hagedorn temperature ''T''<sub>H</sub> = 150 MeV per particle, corresponding to a temperature exceeding 1.66 trillion K. Lead and gold nuclei have been used in such collisions at the CERN [[Super Proton Synchrotron]] and at the Brookhaven [[Relativistic Heavy Ion Collider]], respectively. The nuclei are accelerated to ultrarelativistic speeds, directed toward each other, and create a hot fireball in the rare event of a collision. Hydrodynamic simulations predict that this fireball expands under its own pressure and cools while expanding. Measurements of spherical and elliptic flow test these models.
+Production of QGP in the laboratory is achieved by colliding heavy atomic nuclei, or heavy ions, at relativistic energy. Matter is heated well above the Hagedorn temperature ''T''<sub>H</sub> = 150 MeV per particle, corresponding to a temperature exceeding 1.66 trillion K. Lead and gold nuclei have been used in such collisions at the CERN Super Proton Synchrotron and at the Brookhaven Relativistic Heavy Ion Collider, respectively. The nuclei are accelerated to ultrarelativistic speeds, directed toward each other, and create a hot fireball in the rare event of a collision. Hydrodynamic simulations predict that this fireball expands under its own pressure and cools while expanding. Measurements of spherical and elliptic flow test these models.
 === Diagnostic tools ===
-Quark–gluon plasma is produced in relativistic heavy-ion collisions.<ref>{{Cite journal|last1=Busza|first1=Wit|last2=Rajagopal|first2=Krishna|last3=van der Schee|first3=Wilke|year=2018|title=Heavy ion collisions: The big picture and the big questions|journal=[[Annual Review of Nuclear and Particle Science]]|language=en|volume=68|issue=1|pages=339–376|doi=10.1146/annurev-nucl-101917-020852|doi-access=free|arxiv=1802.04801|s2cid=119264938|issn=0163-8998}}</ref><ref name="ALICE Collaboration-2017">{{Cite journal|last=ALICE Collaboration|year=2017|title=Enhanced production of multi-strange hadrons in high-multiplicity proton–proton collisions|url=[http://www.nature.com/articles/nphys4111|journal=Nature](http://www.nature.com/articles/nphys4111|journal=Nature) Physics|language=en|volume=13|issue=6|pages=535–539|doi=10.1038/nphys4111|arxiv=1606.07424|s2cid=221304738 |issn=1745-2473}}</ref><ref>{{Cite journal|last1=Koch|first1=Peter|last2=Müller|first2=Berndt|last3=Rafelski|first3=Johann|year=2017|title=From strangeness enhancement to quark–gluon plasma discovery|journal=International Journal of Modern Physics A|language=en|volume=32|issue=31|pages=1730024–272|doi=10.1142/S0217751X17300241|arxiv=1708.08115|s2cid=119421190|issn=0217-751X}}</ref><ref name="The WA97 Collaboration-2000">{{Cite journal|last=The WA97 Collaboration|year=2000|title=Transverse mass spectra of strange and multi–strange particles in Pb–Pb collisions at 158 A GeV/c|journal=The European Physical Journal C|language=en|volume=14|issue=4|pages=633–641|doi=10.1007/s100520000386|s2cid=195312472|issn=1434-6044|url=[https://cds.cern.ch/record/429846}}](https://cds.cern.ch/record/429846}})</ref>
+Quark–gluon plasma is produced in relativistic heavy-ion collisions.<ref>{{Cite journal|last1=Busza|first1=Wit|last2=Rajagopal|first2=Krishna|last3=van der Schee|first3=Wilke|year=2018|title=Heavy ion collisions: The big picture and the big questions|journal=Annual Review of Nuclear and Particle Science|language=en|volume=68|issue=1|pages=339–376|doi=10.1146/annurev-nucl-101917-020852|doi-access=free|arxiv=1802.04801|s2cid=119264938|issn=0163-8998}}</ref><ref name="ALICE Collaboration-2017">{{Cite journal|last=ALICE Collaboration|year=2017|title=Enhanced production of multi-strange hadrons in high-multiplicity proton–proton collisions|url=[http://www.nature.com/articles/nphys4111|journal=Nature](http://www.nature.com/articles/nphys4111|journal=Nature) Physics|language=en|volume=13|issue=6|pages=535–539|doi=10.1038/nphys4111|arxiv=1606.07424|s2cid=221304738 |issn=1745-2473}}</ref><ref>{{Cite journal|last1=Koch|first1=Peter|last2=Müller|first2=Berndt|last3=Rafelski|first3=Johann|year=2017|title=From strangeness enhancement to quark–gluon plasma discovery|journal=International Journal of Modern Physics A|language=en|volume=32|issue=31|pages=1730024–272|doi=10.1142/S0217751X17300241|arxiv=1708.08115|s2cid=119421190|issn=0217-751X}}</ref><ref name="The WA97 Collaboration-2000">{{Cite journal|last=The WA97 Collaboration|year=2000|title=Transverse mass spectra of strange and multi–strange particles in Pb–Pb collisions at 158 A GeV/c|journal=The European Physical Journal C|language=en|volume=14|issue=4|pages=633–641|doi=10.1007/s100520000386|s2cid=195312472|issn=1434-6044|url=[https://cds.cern.ch/record/429846}}](https://cds.cern.ch/record/429846}})</ref>
 Important classes of experimental observations include:
-* Thermal [[photon]]s and thermal [[dilepton]]s
+* Thermal [[Physics:Quantum photon|photon]]s and thermal dileptons
-* [[Strangeness production]]
+* Strangeness production
-* [[Elliptic flow]]
+* Elliptic flow
-* [[Jet quenching]]
+* Jet quenching
-* [[J/ψ#J/ψ melting|J/ψ melting]]
+* J/ψ melting
-* [[Hanbury Brown and Twiss effect]] and [[Bose–Einstein correlations]]
+* Hanbury Brown and Twiss effect and Bose–Einstein correlations
-* [[single particle spectrum|Single-particle spectra]]
+* Single-particle spectra
 == Expected properties ==
 === Thermodynamics ===
-The cross-over temperature from the normal hadronic phase to the QGP phase is about {{val|156|u=MeV}}.<ref>A. Bazavov, H.-T. Ding, P. Hegde, O. Kaczmarek, F. Karsch, N. Karthik, E. Laermann, Anirban Lahiri, R. Larsen, S.-T. Li, Swagato Mukherjee, H. Ohno, P. Petreczky, H. Sandmeyer, C. Schmidt, S. Sharma, P. Steinbrecher, Chiral crossover in QCD at zero and non-zero chemical potentials, Physics Letters B, Volume 795, 2019, Pages 15–21, ISSN 0370-2693, [https://doi.org/10.1016/j.physletb.2019.05.013](https://doi.org/10.1016/j.physletb.2019.05.013).</ref> The phenomena involved correspond to an energy density of a little less than {{val|1|u=[[Electronvolt|GeV]]/fm<sup>3</sup>}}. For relativistic matter, pressure and temperature are not independent variables, so the equation of state is a relation between energy density and pressure. This has been found through lattice computations and compared with perturbation theory and string-theory-inspired models. Response functions such as the specific heat and quark-number susceptibilities are active topics of calculation.
+The cross-over temperature from the normal hadronic phase to the QGP phase is about {{val|156|u=MeV}}.<ref>A. Bazavov, H.-T. Ding, P. Hegde, O. Kaczmarek, F. Karsch, N. Karthik, E. Laermann, Anirban Lahiri, R. Larsen, S.-T. Li, Swagato Mukherjee, H. Ohno, P. Petreczky, H. Sandmeyer, C. Schmidt, S. Sharma, P. Steinbrecher, Chiral crossover in QCD at zero and non-zero chemical potentials, Physics Letters B, Volume 795, 2019, Pages 15–21, ISSN 0370-2693, [https://doi.org/10.1016/j.physletb.2019.05.013](https://doi.org/10.1016/j.physletb.2019.05.013).</ref> The phenomena involved correspond to an energy density of a little less than {{val|1|u=GeV/fm<sup>3</sup>}}. For relativistic matter, pressure and temperature are not independent variables, so the equation of state is a relation between energy density and pressure. This has been found through lattice computations and compared with perturbation theory and string-theory-inspired models. Response functions such as the specific heat and quark-number susceptibilities are active topics of calculation.
 === Flow ===
-The discovery of QGP as an almost perfect liquid was a turning point in high-energy nuclear physics. Experiments at RHIC revealed a substance with extremely low resistance to flow.<ref>{{Cite web|url=[https://www.bnl.gov/newsroom/news.php?a=25756|title=Celebrating](https://www.bnl.gov/newsroom/news.php?a=25756|title=Celebrating) a Decade of Brewing Perfection|date=26 June 2015|website=Brookhaven National Laboratory|url-status=live|archive-url=[https://web.archive.org/web/20170628150247/https://www.bnl.gov/newsroom/news.php?a=25756|archive-date=28](https://web.archive.org/web/20170628150247/https://www.bnl.gov/newsroom/news.php?a=25756|archive-date=28) June 2017|access-date=2020-04-15|quote=Berndt Müller, Brookhaven Lab's Associate Laboratory Director for Nuclear and Particle Physics.}}</ref> Nuclear matter at low temperature is known to behave like a superfluid. When heated, the nuclear fluid evaporates into a dilute gas of nucleons and, on further heating, a gas of baryons and mesons. At the critical temperature, hadrons melt and the gas turns back into a liquid. RHIC experiments showed that this liquid has less resistance to flow than any other substance observed in laboratory experiments at any scale. Detailed measurements indicate that it is a quark–gluon plasma in which quarks, antiquarks and gluons flow collectively.<ref>Letter from Berndt Müller to Johann Rafelski, reproduced in "Discovery of Quark–Gluon Plasma: Strangeness Diaries". The European Physical Journal Special Topics. 229 (1): pp.40–41 [[doi:10.1140/epjst/e2019-900263-x]]. ISSN 1951-6401.</ref>
+The discovery of QGP as an almost perfect liquid was a turning point in high-energy nuclear physics. Experiments at RHIC revealed a substance with extremely low resistance to flow.<ref>{{Cite web|url=[https://www.bnl.gov/newsroom/news.php?a=25756|title=Celebrating](https://www.bnl.gov/newsroom/news.php?a=25756|title=Celebrating) a Decade of Brewing Perfection|date=26 June 2015|website=Brookhaven National Laboratory|url-status=live|archive-url=[https://web.archive.org/web/20170628150247/https://www.bnl.gov/newsroom/news.php?a=25756|archive-date=28](https://web.archive.org/web/20170628150247/https://www.bnl.gov/newsroom/news.php?a=25756|archive-date=28) June 2017|access-date=2020-04-15|quote=Berndt Müller, Brookhaven Lab's Associate Laboratory Director for Nuclear and Particle Physics.}}</ref> Nuclear matter at low temperature is known to behave like a superfluid. When heated, the nuclear fluid evaporates into a dilute gas of nucleons and, on further heating, a gas of baryons and mesons. At the critical temperature, hadrons melt and the gas turns back into a liquid. RHIC experiments showed that this liquid has less resistance to flow than any other substance observed in laboratory experiments at any scale. Detailed measurements indicate that it is a quark–gluon plasma in which quarks, antiquarks and gluons flow collectively.<ref>Letter from Berndt Müller to Johann Rafelski, reproduced in "Discovery of Quark–Gluon Plasma: Strangeness Diaries". The European Physical Journal Special Topics. 229 (1): pp.40–41 doi:10.1140/epjst/e2019-900263-x. ISSN 1951-6401.</ref>
 [[File:Schematic representation of the interaction region formed.png|thumb|upright=1.5|Schematic representation of the interaction region formed in the first moments after the collision of high-energy heavy ions.<ref name="Ollitrault-1992" />]]
@@ Line 77: / Line 81: @@
 === Jet quenching effect ===
-Detailed predictions for the production of jets were made in the late 1970s for the CERN [[Super Proton–Antiproton Synchrotron]].<ref>{{Cite journal|last1=Jacob|first1=M.|last2=Landshoff|first2=P.V.|year=1978|title=Large transverse momentum and jet studies|journal=Physics Reports|language=en|volume=48|issue=4|pages=285–350|doi=10.1016/0370-1573(78)90177-1|url=[https://cds.cern.ch/record/262302}}](https://cds.cern.ch/record/262302}})</ref><ref>{{Cite journal|last=Jacob|first=M|year=1979|title=Jets in high energy collisions|journal=Physica Scripta|volume=19|issue=2|pages=69–78|doi=10.1088/0031-8949/19/2/001|s2cid=250809871|issn=0031-8949}}</ref><ref>{{Cite journal|last1=Horgan|first1=R.|last2=Jacob|first2=M.|year=1981|title=Jet production at collider energy|journal=Nuclear Physics B|language=en|volume=179|issue=3|pages=441–460|doi=10.1016/0550-3213(81)90013-4|url=[https://cds.cern.ch/record/134265}}](https://cds.cern.ch/record/134265}})</ref><ref>{{Cite journal|last1=Jacob|first1=M.|last2=Landshoff|first2=P.V.|year=1986|title=Minijets: origin and usefulness|journal=Modern Physics Letters A|language=en|volume=01|issue=12|pages=657–663|doi=10.1142/S021773238600083X|issn=0217-7323|url=[https://cds.cern.ch/record/172538|url-access=subscription}}](https://cds.cern.ch/record/172538|url-access=subscription}})</ref> The UA2 experiment observed the first evidence for jet production in hadron collisions in 1981,<ref>{{Cite journal|last1=Banner|first1=M.|last2=Bloch|first2=Ph.|last3=Bonaudi|first3=F.|last4=Borer|first4=K.|last5=Borghini|first5=M.|last6=Chollet|first6=J.-C.|last7=Clark|first7=A.G.|last8=Conta|first8=C.|last9=Darriulat|first9=P.|last10=Di Lella|first10=L.|last11=Dines-Hansen|first11=J.|year=1982|title=Observation of very large transverse momentum jets at the CERN p collider|journal=Physics Letters B|language=en|volume=118|issue=1–3|pages=203–210|doi=10.1016/0370-2693(82)90629-3|url=[https://cds.cern.ch/record/904153}}](https://cds.cern.ch/record/904153}})</ref> shortly after confirmed by UA1.<ref>{{Cite journal|last1=Arnison|first1=G.|last2=Astbury|first2=A.|last3=Aubert|first3=B.|last4=Bacci|first4=C.|last5=Bernabei|first5=R.|last6=Bézaguet|first6=A.|last7=Böck|first7=R. |last8=Bowcock|first8=T.J.V.|last9=Calvetti|first9=M.|last10=Carroll|first10=T.|last11=Catz|first11=P.|year=1983|title=Observation of jets in high transverse energy events at the CERN proton antiproton collider|journal=Physics Letters B|language=en|volume=123|issue=1–2|pages=115–122|doi=10.1016/0370-2693(83)90970-X|url=[https://cds.cern.ch/record/141936}}](https://cds.cern.ch/record/141936}})</ref>
+Detailed predictions for the production of jets were made in the late 1970s for the CERN Super Proton–Antiproton Synchrotron.<ref>{{Cite journal|last1=Jacob|first1=M.|last2=Landshoff|first2=P.V.|year=1978|title=Large transverse momentum and jet studies|journal=Physics Reports|language=en|volume=48|issue=4|pages=285–350|doi=10.1016/0370-1573(78)90177-1|url=[https://cds.cern.ch/record/262302}}](https://cds.cern.ch/record/262302}})</ref><ref>{{Cite journal|last=Jacob|first=M|year=1979|title=Jets in high energy collisions|journal=Physica Scripta|volume=19|issue=2|pages=69–78|doi=10.1088/0031-8949/19/2/001|s2cid=250809871|issn=0031-8949}}</ref><ref>{{Cite journal|last1=Horgan|first1=R.|last2=Jacob|first2=M.|year=1981|title=Jet production at collider energy|journal=Nuclear Physics B|language=en|volume=179|issue=3|pages=441–460|doi=10.1016/0550-3213(81)90013-4|url=[https://cds.cern.ch/record/134265}}](https://cds.cern.ch/record/134265}})</ref><ref>{{Cite journal|last1=Jacob|first1=M.|last2=Landshoff|first2=P.V.|year=1986|title=Minijets: origin and usefulness|journal=Modern Physics Letters A|language=en|volume=01|issue=12|pages=657–663|doi=10.1142/S021773238600083X|issn=0217-7323|url=[https://cds.cern.ch/record/172538|url-access=subscription}}](https://cds.cern.ch/record/172538|url-access=subscription}})</ref> The UA2 experiment observed the first evidence for jet production in hadron collisions in 1981,<ref>{{Cite journal|last1=Banner|first1=M.|last2=Bloch|first2=Ph.|last3=Bonaudi|first3=F.|last4=Borer|first4=K.|last5=Borghini|first5=M.|last6=Chollet|first6=J.-C.|last7=Clark|first7=A.G.|last8=Conta|first8=C.|last9=Darriulat|first9=P.|last10=Di Lella|first10=L.|last11=Dines-Hansen|first11=J.|year=1982|title=Observation of very large transverse momentum jets at the CERN p collider|journal=Physics Letters B|language=en|volume=118|issue=1–3|pages=203–210|doi=10.1016/0370-2693(82)90629-3|url=[https://cds.cern.ch/record/904153}}](https://cds.cern.ch/record/904153}})</ref> shortly after confirmed by UA1.<ref>{{Cite journal|last1=Arnison|first1=G.|last2=Astbury|first2=A.|last3=Aubert|first3=B.|last4=Bacci|first4=C.|last5=Bernabei|first5=R.|last6=Bézaguet|first6=A.|last7=Böck|first7=R. |last8=Bowcock|first8=T.J.V.|last9=Calvetti|first9=M.|last10=Carroll|first10=T.|last11=Catz|first11=P.|year=1983|title=Observation of jets in high transverse energy events at the CERN proton antiproton collider|journal=Physics Letters B|language=en|volume=123|issue=1–2|pages=115–122|doi=10.1016/0370-2693(83)90970-X|url=[https://cds.cern.ch/record/141936}}](https://cds.cern.ch/record/141936}})</ref>
 The subject was later revived at RHIC. One of the most striking physical effects observed at RHIC energies is jet quenching.<ref>{{Cite journal|last1=Adcox|first1=K.|last2=Adler|first2=S.S.|last3=Afanasiev|first3=S.|last4=Aidala|first4=C.|last5=Ajitanand|first5=N.N.|last6=Akiba|first6=Y.|last7=Al-Jamel|first7=A.|last8=Alexander|first8=J.|last9=Amirikas|first9=R.|last10=Aoki|first10=K.|last11=Aphecetche|first11=L.|year=2005|title=Formation of dense partonic matter in relativistic nucleus–nucleus collisions at RHIC: Experimental evaluation by the PHENIX Collaboration|journal=Nuclear Physics A|language=en|volume=757|issue=1–2|pages=184–283|doi=10.1016/j.nuclphysa.2005.03.086|arxiv=nucl-ex/0410003|s2cid=119511423}}</ref><ref>{{Cite journal|last1=Adams|first1=J.|last2=Aggarwal|first2=M.M.|last3=Ahammed|first3=Z.|last4=Amonett|first4=J.|last5=Anderson|first5=B.D.|last6=Arkhipkin|first6=D.|last7=Averichev|first7=G.S. |last8=Badyal|first8=S.K.|last9=Bai|first9=Y.|last10=Balewski|first10=J.|last11=Barannikova|first11=O.|year=2005|title=Experimental and theoretical challenges in the search for the quark–gluon plasma: The STAR Collaboration's critical assessment of the evidence from RHIC collisions|journal=Nuclear Physics A|language=en|volume=757|issue=1–2|pages=102–183|doi=10.1016/j.nuclphysa.2005.03.085|arxiv=nucl-ex/0501009|s2cid=119062864}}</ref><ref>{{Cite journal|last1=Back|first1=B.B.|last2=Baker|first2=M.D.|last3=Ballintijn|first3=M.|last4=Barton|first4=D.S.|last5=Becker|first5=B.|last6=Betts|first6=R.R.|last7=Bickley|first7=A.A. |last8=Bindel|first8=R.|last9=Budzanowski|first9=A.|last10=Busza|first10=W.|last11=Carroll|first11=A.|year=2005|title=The PHOBOS perspective on discoveries at RHIC|journal=Nuclear Physics A|language=en|volume=757|issue=1–2|pages=28–101|doi=10.1016/j.nuclphysa.2005.03.084|arxiv=nucl-ex/0410022}}</ref> At the first stage of interaction between colliding relativistic nuclei, partons of the colliding nuclei give rise to secondary partons with large transverse momentum. Passing through hot, compressed plasma, these partons lose energy. The magnitude of energy loss depends on QGP properties such as temperature and density. Colored quarks and gluons are the elementary objects of the plasma, so parton energy loss in QGP differs from energy loss in a medium made of colorless hadrons. Under RHIC conditions, parton energy losses are estimated as {{tmath|\frac{dE}{dx} {{=}} 1~\text{GeV/fm} }}. This conclusion is supported by comparing high-transverse-momentum hadron yields in nucleon-nucleon and nucleus-nucleus collisions at the same energy. The reduced yield in nucleus-nucleus collisions suggests that nuclear collisions cannot be regarded as a simple superposition of nucleon-nucleon collisions. For a short time and small volume, quarks and gluons form an almost ideal liquid whose collective properties affect the motion and energy loss of partons.<ref>{{Cite book|last=Schukraft|first=Jürgen|url=[https://indico.cern.ch/event/114939/contributions/62599/attachments/48842/70225/CERN_HI_Dec_2010.pdf|title=ALICE—'Little](https://indico.cern.ch/event/114939/contributions/62599/attachments/48842/70225/CERN_HI_Dec_2010.pdf|title=ALICE—'Little) Bang': The first 3 weeks ...|year=2010}}</ref>
-In November 2010, CERN announced the first direct observation of jet quenching based on heavy-ion collisions.<ref>{{cite press release |title=LHC experiments bring new insight into primordial universe |url=[https://press.web.cern.ch/press-releases/2010/11/lhc-experiments-bring-new-insight-primordial-universe|publisher=[[CERN](https://press.web.cern.ch/press-releases/2010/11/lhc-experiments-bring-new-insight-primordial-universe|publisher=[[CERN)]] |date=November 26, 2010 |access-date=December 2, 2010}}</ref><ref>{{cite journal |last=Aad |first=G. |display-authors=etal |collaboration=ATLAS Collaboration |title=Observation of a Centrality-Dependent Dijet Asymmetry in Lead-Lead Collisions at {{sqrt|s<sub>NN</sub>}} = 2.76 TeV with the ATLAS Detector at the LHC |journal=Physical Review Letters |volume=105 |issue=25 |date=13 December 2010 |doi=10.1103/physrevlett.105.252303 |doi-access=free |article-number=252303 |pmid=21231581 |arxiv=1011.6182 |bibcode=2010PhRvL.105y2303A }}</ref><ref>{{cite journal |last=Chatrchyan |first=S. |display-authors=etal |collaboration=CMS Collaboration |title=Observation and studies of jet quenching in Pb-Pb collisions at {{sqrt|s<sub>NN</sub>}} = 2.76 TeV |journal=Physical Review C |volume=84 |issue=2 |date=12 August 2011 |doi=10.1103/physrevc.84.024906 |doi-access=free |article-number=024906 |arxiv=1102.1957 |bibcode=2011PhRvC..84b4906C }}</ref><ref>{{cite web|url=[http://home.web.cern.ch/about/physics/heavy-ions-and-quark-gluon-plasma|archive-url=https://web.archive.org/web/20121203180310/http://home.web.cern.ch/about/physics/heavy-ions-and-quark-gluon-plasma|url-status=live|archive-date=December](http://home.web.cern.ch/about/physics/heavy-ions-and-quark-gluon-plasma|archive-url=https://web.archive.org/web/20121203180310/http://home.web.cern.ch/about/physics/heavy-ions-and-quark-gluon-plasma|url-status=live|archive-date=December) 3, 2012|title=Heavy ions and quark–gluon plasma|author=CERN|date=18 July 2012}}</ref>
+In November 2010, CERN announced the first direct observation of jet quenching based on heavy-ion collisions.<ref>{{cite press release |title=LHC experiments bring new insight into primordial universe |url=[https://press.web.cern.ch/press-releases/2010/11/lhc-experiments-bring-new-insight-primordial-universe|publisher=[[CERN](https://press.web.cern.ch/press-releases/2010/11/lhc-experiments-bring-new-insight-primordial-universe|publisher=CERN) |date=November 26, 2010 |access-date=December 2, 2010}}</ref><ref>{{cite journal |last=Aad |first=G. |display-authors=etal |collaboration=ATLAS Collaboration |title=Observation of a Centrality-Dependent Dijet Asymmetry in Lead-Lead Collisions at  = 2.76 TeV with the ATLAS Detector at the LHC |journal=Physical Review Letters |volume=105 |issue=25 |date=13 December 2010 |doi=10.1103/physrevlett.105.252303 |doi-access=free |article-number=252303 |pmid=21231581 |arxiv=1011.6182 |bibcode=2010PhRvL.105y2303A }}</ref><ref>{{cite journal |last=Chatrchyan |first=S. |display-authors=etal |collaboration=CMS Collaboration |title=Observation and studies of jet quenching in Pb-Pb collisions at  = 2.76 TeV |journal=Physical Review C |volume=84 |issue=2 |date=12 August 2011 |doi=10.1103/physrevc.84.024906 |doi-access=free |article-number=024906 |arxiv=1102.1957 |bibcode=2011PhRvC..84b4906C }}</ref><ref>{{cite web|url=[http://home.web.cern.ch/about/physics/heavy-ions-and-quark-gluon-plasma|archive-url=https://web.archive.org/web/20121203180310/http://home.web.cern.ch/about/physics/heavy-ions-and-quark-gluon-plasma|url-status=live|archive-date=December](http://home.web.cern.ch/about/physics/heavy-ions-and-quark-gluon-plasma|archive-url=https://web.archive.org/web/20121203180310/http://home.web.cern.ch/about/physics/heavy-ions-and-quark-gluon-plasma|url-status=live|archive-date=December) 3, 2012|title=Heavy ions and quark–gluon plasma|author=CERN|date=18 July 2012}}</ref>
 === Direct photons and dileptons ===
@@ Line 87: / Line 91: @@
 === Glasma hypothesis ===
-Since 2008, physicists have discussed a hypothetical precursor state of QGP called the [[color glass condensate|glasma]], in which dressed particles are condensed into a glassy or amorphous state below the genuine transition between the confined state and the plasma liquid.<ref>{{Cite journal |title=From Glasma to Quark Gluon Plasma in heavy ion collisions |year=2008 |arxiv=0806.1356 |bibcode=2008JPhG...35j4003V |doi=10.1088/0954-3899/35/10/104003 |volume=35 |issue=10 |journal=Journal of Physics G: Nuclear and Particle Physics |article-number=104003|last1=Venugopalan |first1=Raju |s2cid=15121756 }}</ref> This would be analogous to the formation of metallic glasses, or amorphous alloys, below the onset of the liquid metallic state.
+Since 2008, physicists have discussed a hypothetical precursor state of QGP called the glasma, in which dressed particles are condensed into a glassy or amorphous state below the genuine transition between the confined state and the plasma liquid.<ref>{{Cite journal |title=From Glasma to Quark Gluon Plasma in heavy ion collisions |year=2008 |arxiv=0806.1356 |bibcode=2008JPhG...35j4003V |doi=10.1088/0954-3899/35/10/104003 |volume=35 |issue=10 |journal=Journal of Physics G: Nuclear and Particle Physics |article-number=104003|last1=Venugopalan |first1=Raju |s2cid=15121756 }}</ref> This would be analogous to the formation of metallic glasses, or amorphous alloys, below the onset of the liquid metallic state.
 Although the high temperatures and densities predicted to produce QGP have been realized in the laboratory, the resulting matter does not behave as a quasi-ideal state of free quarks and gluons. Instead, it behaves as an almost perfect dense fluid.<ref name="Zajc">{{Cite journal|first=WA|last=Zajc|year=2008|title=The fluid nature of quark–gluon plasma|journal=Nuclear Physics A|volume=805|issue=1–4|pages=283c–294c|arxiv=0802.3552|doi=10.1016/j.nuclphysa.2008.02.285|s2cid=119273920}}</ref> The possibility that QGP would not yet be free at accelerator temperatures was predicted in 1984 as a consequence of remnant effects of confinement.<ref>{{Cite journal|last1=Plümer|first1=M.|last2=Raha|first2=S.|last3=Weiner|first3=R. M.|name-list-style=amp|year=1984|title=How free is the quark–gluon plasma|journal=Nucl. Phys. A|volume=418|pages=549–557|doi=10.1016/0375-9474(84)90575-X}}</ref><ref>{{Cite journal|last1=Plümer|first1=M.|last2=Raha|first2=S.|last3=Weiner|first3=R. M.|name-list-style=amp|year=1984|title=Effect of confinement on the sound velocity in a quark–gluon plasma|journal=Phys. Lett. B|volume=139|issue=3|pages=198–202|doi=10.1016/0370-2693(84)91244-9}}</ref>
 === Neutron stars ===
-It has been hypothesized that the core of some massive [[neutron star]]s may contain deconfined quark matter related to quark–gluon plasma.<ref>{{Cite journal |last1=Annala |first1=Eemeli |last2=Gorda |first2=Tyler |last3=Hirvonen |first3=Joonas |last4=Komoltsev |first4=Oleg |last5=Kurkela |first5=Aleksi |last6=Nättilä |first6=Joonas |last7=Vuorinen |first7=Aleksi |date=2023-12-19 |title=Strongly interacting matter exhibits deconfined behavior in massive neutron stars |journal=Nature Communications |language=en |volume=14 |issue=1 |page=8451 |doi=10.1038/s41467-023-44051-y |pmid=38114461 |issn=2041-1723|pmc=10730725 |arxiv=2303.11356 }}</ref>
+It has been hypothesized that the core of some massive neutron stars may contain deconfined quark matter related to quark–gluon plasma.<ref>{{Cite journal |last1=Annala |first1=Eemeli |last2=Gorda |first2=Tyler |last3=Hirvonen |first3=Joonas |last4=Komoltsev |first4=Oleg |last5=Kurkela |first5=Aleksi |last6=Nättilä |first6=Joonas |last7=Vuorinen |first7=Aleksi |date=2023-12-19 |title=Strongly interacting matter exhibits deconfined behavior in massive neutron stars |journal=Nature Communications |language=en |volume=14 |issue=1 |page=8451 |doi=10.1038/s41467-023-44051-y |pmid=38114461 |issn=2041-1723|pmc=10730725 |arxiv=2303.11356 }}</ref>
 == Onset of deconfinement ==
-The central issue in the formation of quark–gluon plasma is the search for the [[Physics:Quantum deconfinement|onset of deconfinement]]. From the beginning of QGP research, the question was whether sufficient energy density could be achieved in nucleus-nucleus collisions. This depends on how much energy each nucleon loses. An influential reaction picture was the scaling solution presented by [[James Bjorken|Bjorken]].<ref>{{Cite journal|last=Bjorken|first=J. D.|year=1983|title=Highly relativistic nucleus-nucleus collisions: The central rapidity region|journal=Physical Review D|language=en|volume=27|issue=1|pages=140–151|doi=10.1103/PhysRevD.27.140|issn=0556-2821}}</ref> This model applies to ultra-high-energy collisions. In experiments at CERN SPS and BNL RHIC, the situation is usually divided into three stages:<ref name="Letessier-2002">{{Cite book|last1=Letessier|first1=Jean|url=[https://books.google.com/books?id=SAlbKkdor1gC|title=Hadrons](https://books.google.com/books?id=SAlbKkdor1gC|title=Hadrons) and Quark–Gluon Plasma|last2=Rafelski|first2=Johann|author2-link=Johann Rafelski|date=2002-05-30|publisher=Cambridge University Press|isbn=978-1-139-43303-7|language=en|ref=7}}</ref>
+The central issue in the formation of quark–gluon plasma is the search for the onset of deconfinement. From the beginning of QGP research, the question was whether sufficient energy density could be achieved in nucleus-nucleus collisions. This depends on how much energy each nucleon loses. An influential reaction picture was the scaling solution presented by Bjorken.<ref>{{Cite journal|last=Bjorken|first=J. D.|year=1983|title=Highly relativistic nucleus-nucleus collisions: The central rapidity region|journal=Physical Review D|language=en|volume=27|issue=1|pages=140–151|doi=10.1103/PhysRevD.27.140|issn=0556-2821}}</ref> This model applies to ultra-high-energy collisions. In experiments at CERN SPS and BNL RHIC, the situation is usually divided into three stages:<ref name="Letessier-2002">{{Cite book|last1=Letessier|first1=Jean|url=[https://books.google.com/books?id=SAlbKkdor1gC|title=Hadrons](https://books.google.com/books?id=SAlbKkdor1gC|title=Hadrons) and Quark–Gluon Plasma|last2=Rafelski|first2=Johann|author2-link=Johann Rafelski|date=2002-05-30|publisher=Cambridge University Press|isbn=978-1-139-43303-7|language=en|ref=7}}</ref>
 * Primary parton collisions and baryon stopping at the time of complete overlap of the colliding nuclei.
@@ Line 107: / Line 111: @@
 {{div col |colwidth=27em}}
 * [[Physics:Quantum chromodynamics|Quantum chromodynamics]]
-* [[Physics:Quantum confinement|Color confinement]]
+* Color confinement
-* [[Color-glass condensate]]
+* Color-glass condensate
 * [[Physics:Quantum hadron|Hadrons]]
-* [[Hadronization]]
+* Hadronization
-* [[Hagedorn temperature]]
+* Hagedorn temperature
-* [[Neutron star]]
+* Neutron star
 * [[Physics:Quantum matter/plasma|Plasma physics]]
-* [[QCD matter]]
+* QCD matter
 * [[Physics:Quantum electrodynamics|Quantum electrodynamics]]
-* [[Quantum hydrodynamics]]
+* Quantum hydrodynamics
-* [[Relativistic plasma]]
+* Relativistic plasma
-* [[Relativistic nuclear collision]]
+* Relativistic nuclear collision
-* [[Strangeness production]]
+* Strangeness production
-* [[Strange matter]]
+* Strange matter
-* [[List of unsolved problems in physics]]
+* List of unsolved problems in physics
    {{div col end}}
@@ Line 157: / Line 161: @@
 == External links ==
-* {{Commons category-inline}}
+*
 * [[http://www.bnl.gov/rhic/](http://www.bnl.gov/rhic/) The Relativistic Heavy Ion Collider] at [[http://www.bnl.gov/](http://www.bnl.gov/) Brookhaven National Laboratory]
 * [[http://aliceinfo.cern.ch/](http://aliceinfo.cern.ch/) The Alice Experiment] {{Webarchive|url=[https://web.archive.org/web/20110602001439/http://aliceinfo.cern.ch/](https://web.archive.org/web/20110602001439/http://aliceinfo.cern.ch/) |date=2011-06-02 }} at [[https://www.cern.ch/](https://www.cern.ch/) CERN]
@@ Line 166: / Line 170: @@
 * [[https://news.bbc.co.uk/2/hi/science/nature/4462209.stm](https://news.bbc.co.uk/2/hi/science/nature/4462209.stm) BBC article mentioning Brookhaven results (2005)]
 * [[https://web.archive.org/web/20050423224100/http://www.aip.org/pnu/2005/split/728-1.html](https://web.archive.org/web/20050423224100/http://www.aip.org/pnu/2005/split/728-1.html) Physics News Update article on the quark–gluon liquid, with links to preprints]
-* "Hadrons and Quark–Gluon Plasma" by Jean Letessier and [[Johann Rafelski]], Cambridge University Press (2002) {{ISBN|0-521-38536-9}}, Cambridge, UK.
+* "Hadrons and Quark–Gluon Plasma" by Jean Letessier and Johann Rafelski, Cambridge University Press (2002) {{ISBN|0-521-38536-9}}, Cambridge, UK.
-{{Stellar core collapse}}
-{{physics-footer}}
-{{Phase of matter}}
-{{Authority control}}
 =References=

Physics:Quantum Quark–gluon plasma: Difference between revisions

Latest revision as of 22:05, 20 May 2026

History

Role in the Standard Model

Occurrence

Relation to electromagnetic plasma

Theory

Production

Diagnostic tools

Expected properties

Thermodynamics

Flow

Jet quenching effect

Direct photons and dileptons

Glasma hypothesis

Neutron stars

Onset of deconfinement

See also

Table of contents (84 articles)

Index

Full contents

Further reading

Books

Review articles with a historical perspective

External links

References

Navigation menu

Search