This is a constant representing the muon's g factor, the characteristic proportionality constant that relates the muon's magnetic moment, `mu_mu`, to the muon's angular momentum quantum number using the fundamental quantum unit of magnetism.

Notes

The g-factor,  `g_mu`, (also the dimensionless magnetic moment) characterizes the magnetic moment and gyromagnetic ratio of a particle or nucleus.

This constant is specified with a standard uncertainty (standard deviation) of: 0.000 0013