Measurement of the Muonium Hfs Splitting and of the Muon Moment by "Double Resonance," and a New Value ofα

We have determined the hyperfine interval Δν and the muon moment μ_μ=g_μ^_^'μB2 from the frequencies of the two alternative Zeeman transitions in muonium, working at that "magic" field where ∂ν₁∂B=∂ν₂∂B=0. Extrapolating determinations of Δν in Kr and Ar to zero pressure, we obtain consistent results, yielding jointly Δν(0)=4463.3022(89) MHz. Assuming that gⱼ(M) is unshifted by collisions, we obtain gₑg_μ^_^'=206.76509(80), which corresponds to f_μfₚ=3.183373(13). The combination of these results gives α^-1-137=0.03654(30) (2.1 ppm in α^-2), in good agreement with the recommended value of 0.036 02(21).