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Encyclopedia > Gluon
Gluon
Composition: Elementary particle
Family: Boson
Group: Gauge boson
Interaction: Strong interaction
No. of types: 8
Mass: 0
Electric charge: 0
Color charge: nonzero
Spin: 1

In particle physics, gluons are subatomic particles that cause quarks to interact, and are indirectly responsible for the binding of protons and neutrons together in atomic nuclei. In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... In particle physics, bosons, named after Satyendra Nath Bose, are particles having integer spin. ... Gauge bosons are bosonic particles which act as carriers of the fundamental forces of Nature. ... A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ... The invariant mass or intrinsic mass or proper mass or rest mass or just mass is a measurement or calculation of the mass of an object that is the same for all frames of reference. ... The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... In quantum chromodynamics (QCD), color or color charge refers to a certain property of the subatomic particles called quarks. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... Thousands of particles explode from the collision point of two relativistic (100 GeV per ion) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... Helium atom (not to scale) Showing two protons (red), two neutrons (green) and a probability cloud (gray) of two electrons (yellow). ... For other uses of this term, see: Quark (disambiguation) 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ... // Properties [1][2] In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... This article or section does not adequately cite its references or sources. ... The nucleus (atomic nucleus) is the center of an atom. ...


In technical terms, they are vector gauge bosons that mediate strong color charge interactions of quarks in quantum chromodynamics (QCD). Unlike the neutral photon of quantum electrodynamics (QED), gluons themselves participate in strong interactions. The gluon has the ability to do this as it carries the color charge and so interacts with itself, making QCD significantly harder to analyse than QED. Vector field given by vectors of the form (-y, x) In mathematics a vector field is a construction in vector calculus which associates a vector to every point in a Euclidean space. ... Gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... Gauge bosons are bosonic particles which act as carriers of the fundamental forces of Nature. ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ... In quantum chromodynamics (QCD), color or color charge refers to a certain property of the subatomic particles called quarks. ... These are the six flavors of quarks and their most likely decay modes. ... Quantum chromodynamics (QCD) is the theory of the strong interaction, a fundamental force describing the interactions of the quarks and gluons found in nucleons (such as the proton and neutron). ... The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, microwaves, radio waves, and visible light are all forms of light. ... Quantum electrodynamics (QED) is a relativistic quantum field theory of electromagnetism. ...

Contents

Properties

The gluon is a vector boson; like the photon, it has a spin of 1. While massive spin-1 particles have three polarization states, massless gauge bosons like the gluon have only two polarization states because gauge invariance requires the polarization to be transverse. In quantum field theory, unbroken gauge invariance requires that gauge bosons have zero mass (experiment limits the gluon's mass to less than a few MeV). The gluon has negative intrinsic parity and zero isospin. It is its own antiparticle. The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, microwaves, radio waves, and visible light are all forms of light. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... Gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... Quantum field theory (QFT) is the application of quantum mechanics to fields. ... In physics, a parity transformation (also called parity inversion) is the simultaneous flip in the sign of all spatial coordinates: A 3×3 matrix representation of P would have determinant equal to –1, and hence cannot reduce to a rotation. ... Isospin (isotopic spin, isobaric spin) is a physical quantity which is mathematically analogous to spin. ... Corresponding to most kinds of particle, there is an associated antiparticle with the same mass and opposite charges. ...


Numerology of gluons

Unlike the single photon of QED or the three W and Z bosons of the weak interaction, there are eight independent types of gluon in QCD. The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, microwaves, radio waves, and visible light are all forms of light. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature. ...


This may be difficult to understand intuitively. Quarks may carry three types of color charge; antiquarks carry three types of anticolor. Gluons may be thought of as carrying both color and anticolor or as describing how quark color changes during interactions, so because gluons carry nonzero color charge it may be thought that there are only six gluons. These are the six flavors of quarks and their most likely decay modes. ... In quantum chromodynamics (QCD), color or color charge refers to a certain property of the subatomic particles called quarks. ...


Technically, QCD is a gauge theory with SU(3) gauge symmetry. Quarks are introduced as spinor fields in Nf flavours, each in the fundamental representation (triplet, denoted 3) of the colour gauge group, SU(3). The gluons are vector fields in the adjoint representation (octets, denoted 8) of colour SU(3). For a general gauge group, the number of force-carriers (like photons or gluons) is always equal to the dimension of the adjoint representation. For the simple case of SU(N), the dimension of this representation is N2−1. In physics, gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... In mathematics, the special unitary group of degree n is the group of n by n unitary matrices with determinant 1 and entries from the field C of complex numbers, with the group operation that of matrix multiplication. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Flavour (or flavor) is a quantum number of elementary particles related to their weak interactions. ... In mathematics, a fundamental representation is a representation of a mathematical structure, such as a group, that satisfies the following condition: All other irreducible representations of the group can be found in the tensor products of the fundamental representation with many copies of itself. ... In mathematics, the adjoint representation (or adjoint action) of a Lie group G is the natural representation of G on its own Lie algebra. ... In mathematics, a Lie group is a group whose elements can be continuously parametrized by real numbers, such as the rotation group, which can be parametrized by the Euler angles. ...


Confinement

Main article: Colour confinement

Since gluons themselves carry color charge (again, unlike the photon which is electrically neutral), they participate in strong interactions. These gluon-gluon interactions constrain color fields to string-like objects called "flux tubes", which exert constant force when stretched. Due to this force, quarks are confined within composite particles called hadrons. This effectively limits the range of the strong interaction to 10-15 meters, roughly the size of an atomic nucleus. Colour confinement (often just confinement) is the physics phenomenon that color charged particles (such as quarks) cannot be isolated. ... The word light is defined here as electromagnetic radiation of any wavelength; thus, X-rays, gamma rays, ultraviolet light, microwaves, radio waves, and visible light are all forms of light. ... These are the six flavors of quarks and their most likely decay modes. ... Colour confinement (often just confinement) is the physics phenomenon that color charged particles (such as quarks) cannot be isolated. ... Elementary particles An elementary particle is a particle with no measurable internal structure, that is, it is not a composite of other particles. ... In particle physics, a hadron is a subatomic particle which experiences the nuclear force. ... The metre, or meter (symbol: m) is the SI base unit of length. ... A semi-accurate depiction of the helium atom. ...


Gluons also share this property of being confined within hadrons. One consequence is that gluons are not directly involved in the nuclear forces. The force mediators for these are other hadrons called mesons. The nuclear force (or nucleon-nucleon interaction or residual strong force) is the force between two or more nucleons. ... Mesons of spin 1 form a nonet In particle physics, a meson is a strongly interacting boson, that is, it is a hadron with integral spin. ...


Although in the normal phase of QCD single gluons may not travel freely, it is predicted that there exist hadrons which are formed entirely of gluons — called glueballs. There are also conjectures about other exotic hadrons in which real gluons (as opposed to virtual ones found in ordinary hadrons) would be primary constituents. Beyond the normal phase of QCD (at extreme temperatures and pressures), quark gluon plasma forms. In such a plasma there are no hadrons; quarks and gluons become free particles. The QCD vacuum is the vacuum state of Quantum chromodynamics (QCD). ... In particle physics, a hadron is a subatomic particle which experiences the nuclear force. ... In particle physics, a glueball is a particle containing no valence quarks. ... A regular meson made from a quark (q) and antiquark (q-bar) with spins s2 and s1 respectively and having an overall angular momentum L Exotic hadrons are subatomic particles made of quarks (and possibly gluons), but which do not fit into the usual schema of hadrons. ... In physics, a virtual particle is a particle which exists for such a short time and space that its energy and momentum do not have to obey the usual relationship. ... Quark gluon plasma is a phase of Quantum Chromodynamics (QCD) which exists at extremely high temperature and density. ...


Experimental observations

The first direct experimental evidence of gluons was found in 1979 when three-jet events were observed at the electron-positron collider called PETRA at DESY in Hamburg. Quantitative studies of deep inelastic scattering at the Stanford Linear Accelerator Center had established their existence a decade before that. For the song by the Smashing Pumpkins, see 1979 (song). ... The term three jet event, or Mercedes event, refers to particularly distinctive three-jet events found in particle detectors that constitute the most direct evidence currently available for the existence of gluons. ... The current version of this article or section is written in an informal style and with a personally invested tone. ... The DESY (Deutsches Elektronen Synchrotron, German Electron Synchrotron) is the biggest German research center for particle physics, with sites in Hamburg and Zeuthen. ... Hamburg from above Hamburgs motto: May the posterity endeavour with dignity to conserve the freedom, which the forefathers acquired. ... Deep Inelastic Scattering is the name given to a process used to probe the insides of hadrons (particularly the baryons, such as protons and neutrons), using electrons. ... The Stanford Linear Accelerator Center (SLAC) is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Department of Energy Office of Science. ...


Experimentally, confinement is verified by the failure of free quark searches. Neither free quarks nor free gluons have ever been observed. Although there have been hints of exotic hadrons, no glueball has been observed either. Quark-gluon plasma has been found recently at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratories (BNL). These are the six flavors of quarks and their most likely decay modes. ... The Relativistic Heavy Ion Collider at Brookhaven National Laboratory. ... Aerial view of Brookhaven National Laboratory. ...


See also

These are the six flavors of quarks and their most likely decay modes. ... In particle physics, a hadron is a subatomic particle which experiences the nuclear force. ... Gauge bosons are bosonic particles which act as carriers of the fundamental forces of Nature. ... In particle physics, a glueball is a particle containing no valence quarks. ... A regular meson made from a quark (q) and antiquark (q-bar) with spins s2 and s1 respectively and having an overall angular momentum L Exotic hadrons are subatomic particles made of quarks (and possibly gluons), but which do not fit into the usual schema of hadrons. ... In physics, the quark model is a classification scheme for hadrons in terms of their valence quarks, ie, the quarks (and antiquarks) which give rise to the quantum numbers of the hadrons. ... Quantum chromodynamics (QCD) is the theory of the strong interaction, a fundamental force describing the interactions of the quarks and gluons found in nucleons (such as the proton and neutron). ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... The term three jet event, or Mercedes event, refers to particularly distinctive three-jet events found in particle detectors that constitute the most direct evidence currently available for the existence of gluons. ... Deep Inelastic Scattering is the name given to a process used to probe the insides of hadrons (particularly the baryons, such as protons and neutrons), using electrons. ...

References and external links

 v  d  e 
Particles in physics - elementary particles
Fermions: Quarks: (Up · Down · Strange · Charm · Bottom · Top) | Leptons: (Electron · Muon · Tau · Neutrinos)
Gauge bosons: Photon | W and Z bosons | Gluons
Not yet observed: Higgs boson | Graviton | Other hypothetical particles

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