Editing Quark (section)

=== Other phases of quark matter ===
{{Main|QCD matter}}
[[File:QCDphasediagram.svg|upright=1.15|thumb|A qualitative rendering of the [[phase diagram]] of quark matter. The precise details of the diagram are the subject of ongoing research.<ref name=Ruester>
{{cite journal
 |author1=S. B. Rüester
 |author2=V. Werth
 |author3=M. Buballa
 |author4=I. A. Shovkovy
 |author5=D. H. Rischke
 |title=The Phase Diagram of Neutral Quark Natter: Self-consistent Treatment of Quark Masses
 |journal=[[Physical Review D]]
 |volume=72 |issue=3 |page=034003
 |year=2005
 |arxiv=hep-ph/0503184
 |bibcode = 2005PhRvD..72c4004R
 |doi=10.1103/PhysRevD.72.034004
 |s2cid=10487860
}}</ref><ref name=Alford>
{{cite journal
 |author1=M. G. Alford
 |author2=K. Rajagopal
 |author3=T. Schaefer
 |author4=A. Schmitt
 |title=Color Superconductivity in Dense Quark Matter
 |journal=[[Reviews of Modern Physics]]
 |volume=80 |issue=4 |pages=1455–1515
 |year=2008
 |arxiv=0709.4635
 |bibcode = 2008RvMP...80.1455A
 |doi=10.1103/RevModPhys.80.1455
 |s2cid=14117263
}}</ref>|alt=Quark–gluon plasma exists at very high temperatures; the hadronic phase exists at lower temperatures and baryonic densities, in particular nuclear matter for relatively low temperatures and intermediate densities; color superconductivity exists at sufficiently low temperatures and high densities.]]

Under sufficiently extreme conditions, quarks may become "deconfined" out of bound states and propagate as thermalized "free" excitations in the larger medium. In the course of [[asymptotic freedom]], the strong interaction becomes weaker at increasing temperatures. Eventually, color confinement would be effectively lost in an extremely hot [[plasma (physics)|plasma]] of freely moving quarks and gluons. This theoretical phase of matter is called [[quark–gluon plasma]].<ref>
{{cite journal
 |author=S. Mrowczynski
 |journal=[[Acta Physica Polonica B]]
 |title=Quark–Gluon Plasma
 |volume=29 |issue=12
 | page=3711
 |year=1998
 |arxiv=nucl-th/9905005
 |bibcode=1998AcPPB..29.3711M |bibcode-access=free
}}</ref>

The exact conditions needed to give rise to this state are unknown and have been the subject of a great deal of speculation and experimentation. An estimate puts the needed temperature at {{val|1.90|0.02|e=12}} [[kelvin]].<ref>
{{cite journal
 |author1=Z. Fodor
 |author2=S. D. Katz
 |title=Critical Point of QCD at Finite T and μ, Lattice Results for Physical Quark Masses
 |journal=[[Journal of High Energy Physics]]
 |volume=2004 |issue=4 |page=50
 |year=2004
 |arxiv=hep-lat/0402006
 |bibcode=2004JHEP...04..050F
 |doi=10.1088/1126-6708/2004/04/050 |doi-access=free
}}</ref> While a state of entirely free quarks and gluons has never been achieved (despite numerous attempts by [[CERN]] in the 1980s and 1990s),<ref>
{{cite arXiv
 |author1=U. Heinz
 |author2=M. Jacob
 |year=2000
 |title=Evidence for a New State of Matter: An Assessment of the Results from the CERN Lead Beam Programme
 |eprint=nucl-th/0002042
}}</ref> recent experiments at the [[Relativistic Heavy Ion Collider]] have yielded evidence for liquid-like quark matter exhibiting "nearly perfect" [[fluid motion]].<ref name=RHIC>
{{cite web
 |year         = 2005
 |title        = RHIC Scientists Serve Up "Perfect" Liquid
 |url          = https://www.bnl.gov/rhic/news2/news.asp?a=303&t=pr
 |access-date   = 2009-05-22
 |publisher    = [[Brookhaven National Laboratory]]
 |archive-url  = https://web.archive.org/web/20130415062818/http://www.bnl.gov/rhic/news2/news.asp?a=303&t=pr
 |archive-date = 2013-04-15
}}</ref>

The quark–gluon plasma would be characterized by a great increase in the number of heavier quark pairs in relation to the number of up and down quark pairs. It is believed that in the period prior to 10<sup>−6</sup> seconds after the [[Big Bang]] (the [[quark epoch]]), the universe was filled with quark–gluon plasma, as the temperature was too high for hadrons to be stable.<ref>
{{cite book
 |author=T. Yulsman
 |title=Origins: The Quest for Our Cosmic Roots
 |page=75
 |publisher=[[CRC Press]]
 |year=2002
 |isbn=978-0-7503-0765-9
}}</ref>

Given sufficiently high baryon densities and relatively low temperatures – possibly comparable to those found in [[neutron star]]s – quark matter is expected to degenerate into a [[Fermi liquid]] of weakly interacting quarks. This liquid would be characterized by a [[condensation]] of colored quark [[Cooper pair]]s, thereby [[spontaneous symmetry breaking|breaking the local SU(3)<sub>c</sub> symmetry]]. Because quark Cooper pairs harbor color charge, such a phase of quark matter would be [[color superconductivity|color superconductive]]; that is, color charge would be able to pass through it with no resistance.<ref>
{{cite book
 |author1=A. Sedrakian
 |author2=J. W. Clark
 |author3=M. G. Alford
 |title=Pairing in Fermionic Systems
 |url=https://archive.org/details/pairingfermionic00sedr
 |url-access=limited
 |pages=[https://archive.org/details/pairingfermionic00sedr/page/n12 2]–3
 |publisher=[[World Scientific]]
 |year=2007
 |isbn=978-981-256-907-3
}}</ref>

{{Portal|Physics}}