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 Δν 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_μfₚ=3.183338(13) this implies (a) α^-1-137=0.03619(30) (2.2 ppm) and (b) a proton polarizability δN⁽²⁾=-(4±4) ppm.