Magnetic Moment of the Positive Muon

The magnetic moment of the positive muon has been redetermined in terms of proton moments using a precession technique. The sensitivity achieved yields an error of 13 parts per million. The muons are stopped in various targets in a homogeneous magnetic field. The anisotropic distribution of the decay electrons relative to the muon spin direction permits the measurement of the spin precession frequency. The proton spin resonance is measured in the same field, yielding $\frac{f_{\mu }}{f_p}=3.18338\mathrm{}\pm 0.00004$. This result may be combined with that of other experiments, the muon $g$ factor, and the ratio of electron cyclotron frequency to proton resonance, $\frac{f_e}{f_p}$, to obtain a more precise evaluation of the muon mass in terms of electron masses. $\frac{m_{\mu }}{m_e}$ equals 206.765±0.005.