New Measurement of the Anomalous Magnetic Moment of the Positive Muon

The muon anomalous magnetic moment has been measured in a new experiment at Brookhaven. Polarized muons were stored in a superferric ring, and the angular frequency difference, ${\ensuremath{\omega}}_{a}$, between the spin precession and orbital frequencies was determined by measuring the time distribution of high-energy decay positrons. The ratio $R$ of ${\ensuremath{\omega}}_{a}$ to the Larmor precession frequency of free protons, ${\ensuremath{\omega}}_{p}$, in the storage-ring magnetic field was measured. We find $R\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3.707220(48)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. With ${\ensuremath{\mu}}_{\ensuremath{\mu}}/{\ensuremath{\mu}}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3.18334547(47)$ this gives ${a}_{{\ensuremath{\mu}}^{+}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1165925(15)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ ( $\ifmmode\pm\else\textpm\fi{}13\mathrm{ppm}$), in good agreement with the previous CERN measurements for ${\ensuremath{\mu}}^{+}$ and ${\ensuremath{\mu}}^{\ensuremath{-}}$ and of approximately the same precision.