Color-glass condensate (CGC) is a type of

matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic pa ...

theorized to exist in

atomic nuclei The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford at the University of Manchester based on the 1909 Geiger–Marsden gold foil experiment. Aft ...

when they collide at near the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...

. During such collision, one is sensitive to the

gluons A gluon ( ) is a type of massless elementary particle that mediates the strong interaction between quarks, acting as the exchange particle for the interaction. Gluons are massless vector bosons, thereby having a spin of 1. Through the s ...

that have very small momenta, or more precisely a very small Bjorken scaling variable. The small momenta gluons dominate the description of the collision because their

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

is very large. This is because a high-momentum gluon is likely to split into smaller momentum gluons. When the gluon density becomes large enough, gluon-gluon recombination puts a limit on how large the gluon density can be. When gluon recombination balances gluon splitting, the density of gluons saturate, producing new and universal properties of hadronic matter. This state of saturated gluon matter is called the color-glass condensate. "Color" in the name "color-glass condensate" refers to a type of charge that

quark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...

s and gluons carry as a result of the

strong nuclear force In nuclear physics and particle physics, the strong interaction, also called the strong force or strong nuclear force, is one of the four known fundamental interactions. It confines quarks into protons, neutrons, and other hadron particles, an ...

. The word "

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

" is borrowed from the term for

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

and other materials that are disordered and act like

solid Solid is a state of matter where molecules are closely packed and can not slide past each other. Solids resist compression, expansion, or external forces that would alter its shape, with the degree to which they are resisted dependent upon the ...

s on short time scales but

liquid Liquid is a state of matter with a definite volume but no fixed shape. Liquids adapt to the shape of their container and are nearly incompressible, maintaining their volume even under pressure. The density of a liquid is usually close to th ...

s on long time scales. In the CGC

phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform *Phase space, a mathematica ...

, the gluons themselves are disordered and do not change their positions rapidly. "Condensate" means that the gluons have a very high density. The color-glass condensate describes an

intrinsic In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, mass i ...

property of matter that can only be observed under high-energy conditions such as those at RHIC, the

Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It was built by the CERN, European Organization for Nuclear Research (CERN) between 1998 and 2008, in collaboration with over 10,000 scientists, ...

as well as the future Electron Ion Collider.A. Accardi et al., “Electron Ion Collider: The Next QCD Frontier – Understanding the glue that binds us all,”
2012. The color-glass condensate is important because it is proposed as a universal form of matter that describes the properties of all high-energy, strongly interacting particles. It has simple properties that follow from first principles in the theory of strong interactions,

quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is the study of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type of ...

. It has the potential to explain many unsolved problems such as how particles are produced in high-energy collisions, and the distribution of matter itself inside of these particles. Researchers at CERN believe they have created color-glass condensates during collisions of

protons A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' ( elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an electron (the pro ...

with

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

ions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

. In these sorts of collisions, the standard outcome is that new particles are created and fly off in different directions. However, the Compact Muon Solenoid (CMS) team at the LHC found that in a sample of 2 million lead-proton collisions, some pairs of particles flew away from each other with their respective directions correlated. This correlation of directions is the anomaly that might be caused by the existence of a color-glass condensate while the particles are colliding.

Erroneous description in term of hadronic pancakes or gluonic wall

The high density of gluon seen during the collision is often explained by

contraction Contraction may refer to: Linguistics * Contraction (grammar), a shortened word * Poetic contraction, omission of letters for poetic reasons * Elision, omission of sounds ** Syncope (phonology), omission of sounds in a word * Synalepha, merged ...

of the nucleus. Accordingly, this one would appear compressed along its direction of

motion In physics, motion is when an object changes its position with respect to a reference point in a given time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed, and frame of reference to an o ...

and as a result, the

gluon A gluon ( ) is a type of Massless particle, massless elementary particle that mediates the strong interaction between quarks, acting as the exchange particle for the interaction. Gluons are massless vector bosons, thereby having a Spin (physi ...

s inside the nucleus would appear to a stationary

observer An observer is one who engages in observation or in watching an experiment. Observer may also refer to: Fiction * ''Observer'' (novel), a 2023 science fiction novel by Robert Lanza and Nancy Kress * ''Observer'' (video game), a cyberpunk horr ...

as a "gluonic wall" traveling near the

. At very high energies, the

of the gluons in this wall would then increase greatly. However, this description is incorrect for two reasons: . J. Brodsky (2015) “Novel Perspectives from Light-Front QCD, Super-Conformal Algebra, and Light-Front Holography”Bled Workshops Phys. 16 (2015) 2, 35–46 rXiv:1512.05100/ref> #Such description depends on the

frame A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent. Frame and FRAME may also refer to: Physical objects In building construction *Framing (con ...

and therefore violates

Lorentz invariance In a relativistic theory of physics, a Lorentz scalar is a scalar expression whose value is invariant under any Lorentz transformation. A Lorentz scalar may be generated from, e.g., the scalar product of vectors, or by contracting tensors. While ...

: a ''fundamental'' description of the structure of an object cannot depend on a choice of frame. A classical analogy would be if one would provide a ''fundamental'' description using

fictitious force A fictitious force, also known as an inertial force or pseudo-force, is a force that appears to act on an object when its motion is described or experienced from a non-inertial reference frame, non-inertial frame of reference. Unlike real forc ...

s such as the

Coriolis force In physics, the Coriolis force is a pseudo force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the left of the motio ...

. #

is not observable in collision experiments due to the Penrose–Terrell effect. A correct description of the collision can be given using light-front

wave function In quantum physics, a wave function (or wavefunction) is a mathematical description of the quantum state of an isolated quantum system. The most common symbols for a wave function are the Greek letters and (lower-case and capital psi (letter) ...

s,P. A. M. Dirac, (1949) “Forms of Relativistic Dynamics”
Rev. Mod. Phys. 21, 392–399 . J. Brodsky, H. C. Pauli and S. S. Pinsky, (1998) "Quantum chromodynamics and other field theories on the light cone" Phys. Rep. 301 299–486 [arXiv:hep-ph/9705477/ref> which are frame-independent.

References

"Background on color glass condensate"
Brookhaven National Laboratory. *McLerran, Larry (April 26, 2001)
"The Color Glass Condensate and Small x Physics: 4 Lectures"
*Iancu, Edmond; Venugopalan, Raju (March 24, 2003)
"The Color Glass Condensate and High Energy Scattering in QCD"
*Weigert, Heribert (January 11, 2005)
"Evolution at small x_bj: The Color Glass Condensate"
*Riordon, James; Schewe, Phil; Stein, Ben (January 14, 2004)

aip.org. *Moskowitz, Clara (November 27, 2012)

HuffingtonPost.com *Trafton, Anne (November 27, 2012)

MITnews.

External links

* {{States of matter Quantum chromodynamics Nuclear physics

Erroneous description in term of hadronic pancakes or gluonic wall

See also

See also

References

External links