Precision Measurement of the Hyperfine Interval of Muonium by a Novel Technique: Ramsey Resonance in Zero Field

A novel method for measuring the hyperfine interval Δ ν of muonium in "zero" magnetic field is described. It consists in applying two successive coherent microwave pulses (lengths τ, separation T) to muonium, and observing the change in muon polarization at t>T+2τ. By extrapolating two low-pressure runs in Kr we obtain Δν(0)=4463.3013(40) MHz, while a joint fit with earlier Chicago Kr data gives Δν(0)=4463.3012(23) (0.5 ppm). With f_μf_p=3.183 338(13) this implies (a) α^-1-137=0.036 19(30) (2.2 ppm) and (b) a proton polarizability δ_N⁽²⁾=-(4+/-4) ppm.