What is physical significance of g factor?

In summary: I think this is all I wanted to say.In summary, the g factor is a dimensionless number that is useful in comparing the magnetric moments of different particles. It was introduced by Goudsmit and Uhlenbeck to account for the behavior of an electron in a magnetic field. It was found to have a theoretical basis and has a value of 2.
  • #36
Both the muon and electron are (supposed to be) point structureless leptons. Therefore, the g factor due to internal QM should be the same. The g factor should then be
g = 2( 1 + α/2π) = 2.002322819454
including only the external vertex correction.

The electron g factor is 0.000 003 515 lower, and

the muon g factor is 0.000 009 021 higher.

These disparities are due to external radiative corrections. The muon is higher than the electron primarily because the electron-positron vacuum polarization (2 Feynman bubbles) correction is much higher in the muon case than in the electron case.
Bob S

signs corrected 11/19/09
 
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