Improved measurement of the positive muon anomalous magnetic moment

A new measurement of the positive muon's anomalous magnetic moment has been made at the Brookhaven Alternating Gradient Synchrotron using the direct injection of polarized muons into the superferric storage ring. The angular frequency difference ωₐ between the angular spin precession frequency ωₛ and the angular orbital frequency ωc is measured as well as the free proton NMR frequency ωₚ. These determine R=ωₐ/ωₚ=3.707201(19)×10^-3. With μ_μ/μₚ=3.18334539(10) this gives a_μ⁺=11659191(59)×10^-10 (±5 ppm), in good agreement with the previous CERN and BNL measurements for μ⁺ and μ^-, and with the standard model prediction.