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GfactorTemplate:DISPLAYTITLE:gfactor
A gfactor (also called g value or dimensionless magnetic moment) is a dimensionless quantity which characterizes the magnetic moment and gyromagnetic ratio of a particle or nucleus. It is essentially a proportionality constant that relates the observed magnetic moment μ of a particle to the appropriate angular momentum quantum number and the fundamental quantum unit of magnetism, the Bohr magneton. Additional recommended knowledge
Electron gfactorsThere are three magnetic moments associated with an electron: One from its spin angular momentum, one from its orbital angular momentum, and one from its total angular momentum (the quantummechanical sum of those two components). Corresponding to these three moments are three different gfactors: Electron spin gfactorThe most famous of these is the electron spin gfactor, g_{S} (more often called simply the electron gfactor, g_{e}), defined by where μ_{S} is the total magnetic moment resulting from the spin of an electron, S is the magnitude of its spin angular momentum, and μ_{B} is the Bohr magneton. The zcomponent of the magnetic moment then becomes The value g_{S} is roughly equal to two, and is known to extraordinary accuracy.^{[1]}^{[2]} The reason it is not precisely two is explained by quantum electrodynamics.^{[3]} Electron orbital gfactorSecondly, the electron orbital gfactor, g_{L}, is defined by where μ_{L} is the total magnetic moment resulting from the orbital angular momentum of an electron, L is the magnitude of its orbital angular momentum, and μ_{B} is the Bohr magneton. The value of g_{L} is exactly equal to one, by a quantummechanical argument analogous to the derivation of the classical magnetogyric ratio. For an electron in an orbital with a magnetic quantum number m_{l}, the zcomponent of the orbital angular momentum is which, since g_{L} = 1, is just μ_{B}m_{l} Landé gfactorThirdly, the Landé gfactor, g_{J}, is defined by where μ is the total magnetic moment resulting from both spin and orbital angular momentum of an electron, J = L+S is its total angular momentum, and μ_{B} is the Bohr magneton. The value of g_{J} is related to g_{L} and g_{S} by a quantummechanical argument; see the article Landé gfactor. Nucleon and Nucleus gfactorsProtons, neutrons, and many nuclei have spin and magnetic moments, and therefore associated gfactors. The formula conventionally used is where μ is the magnetic moment resulting from the nuclear spin, I is the nuclear spin angular momentum, and μ_{p} is the nuclear magneton. Muon gfactorThe muon, like the electron has a gfactor from its spin, given by the equation where μ is the magnetic moment resulting from the muon’s spin, S is the spin angular momentum, and m_{μ} is the muon mass.
The muon gfactor can be affected by physics beyond the Standard Model, so has been measured very precisely, in particular at the Brookhaven National Laboratory. As of November 2006, the experimentally measured value is 2.0023318416 with an uncertainy of 0.0000000013, compared to the theoretical prediction of 2.0023318361 with an uncertainty of 0.0000000010^{[4]}. This is a difference of 3.4 standard deviations, suggesting beyondtheStandardModel physics may be having an effect. Measured gfactor Values
It should be noted that the electron gfactor is one of the most precisely measured values in physics, with its uncertainty beginning at the twelfth decimal place. Notes and references
See also


This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Gfactor". A list of authors is available in Wikipedia. 