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 partic ...

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 based on the 1909 Geiger–Marsden gold foil experiment. After the discovery of the neutron ...

when they collide at near the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...

. During such collision, one is sensitive to the

gluons A gluon ( ) is an elementary particle that acts as the exchange particle (or gauge boson) for the strong force between quarks. It is analogous to the exchange of photons in the electromagnetic force between two charged particles. Gluons bind qu ...

that have very small momenta, or more precisely a very small

Bjorken scaling James Daniel "BJ" Bjorken (born 1934) is an American theoretical physicist. He was a Putnam Fellow in 1954, received a BS in physics from MIT in 1956, and obtained his PhD from Stanford University in 1959. He was a visiting scholar at the Inst ...

variable. The small momenta gluons dominate the description of the collision because their

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

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 nuclei. All commonly o ...

s and gluons carry as a result of the

strong nuclear force The strong interaction or strong force is a fundamental interaction that confines quarks into proton, neutron, and other hadron particles. The strong interaction also binds neutrons and protons to create atomic nuclei, where it is called the n ...

. The word "

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...

" is borrowed from the term for

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

and other materials that are disordered and act like

solid Solid is one of the State of matter#Four fundamental states, four fundamental states of matter (the others being liquid, gas, and Plasma (physics), plasma). The molecules in a solid are closely packed together and contain the least amount o ...

s on short time scales but

liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...

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 mathematic ...

, 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 ...

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 collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundred ...

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 theory 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 ...

. 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 that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

with

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

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 conven ...

. 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 the phenomenon in which an object changes its position with respect to time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed and frame of reference to an observer and mea ...

and as a result, the

gluon A gluon ( ) is an elementary particle that acts as the exchange particle (or gauge boson) for the strong force between quarks. It is analogous to the exchange of photons in the electromagnetic force between two charged particles. Gluons bind q ...

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: Computer science and information theory * In information theory, any system which receives information from an object * State observer in con ...

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 an expression, formed from items of the theory, which evaluates to a scalar, invariant under any Lorentz transformation. A Lorentz scalar may be generated from e.g., the scalar product of ...

: 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 is a force that appears to act on a mass whose motion is described using a non-inertial frame of reference, such as a linearly accelerating or rotating reference frame. It is related to Newton's second law of motion, which trea ...

s such as the

Coriolis force In physics, the Coriolis force is an inertial or fictitious 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 ...

. #

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 A wave function in quantum physics is a mathematical description of the quantum state of an isolated quantum system. The wave function is a complex-valued probability amplitude, and the probabilities for the possible results of measurements mad ...

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_Lorentz_covariance.html" ;"title="rXiv:hep-ph/9705477.html" ;"title=". 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">. 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 Lorentz covariance">frame-independent.

References

"Background on color glass condensate"

Brookhaven National Laboratory Brookhaven National Laboratory (BNL) is a United States Department of Energy national laboratory located in Upton, Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base and Japanese internment c ...

. *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

References

External links