Longitudinal field quenching studies in KCl and KBr — Evidence for a precursor muonium state

The repolarization of μ⁺ in a longitudinal field as a function of field strength has been measured at various temperatures in KCl and KBr single crystals. The data at room temperature in KCl are essentially in agreement with Ivanteret al. /1/ and Nishiyamaet al. /5/. The obtained quenching curves can be reasonably fitted by assuming that the long lived muonium state, seen directly in transverse field experiments by Kieflet al. /4/, is preceded by another short lived muonium state with reduced hf-coupling. It is also necessary to allow for electron spin exchange in the precursor state. The model fits yield the hyperfine frequency of the precursor state, its chemical lifetime and an electron spin flip rate. It is speculated that the precursor state and the temperature dependence of the fitted parameters reflect the early history of the μ⁺ in its terminal spur.