A new precision measurement of the muonium hyperfine interval in argon

Abstract We have measured the muonium hyperfine interval Δ v in argon at 1802 torr, and find Δv = 4463.2653(24) MHz. The extrapolation to zero density yields perfect agreement with Δ v measured with comparable accuracy in krypton. The argon and krypton results are therefore combined to give a new world average of Δv = 4463.3040(18) MHz.