The transition from Mu to Mu * in diamond

Evidence is presented for a transition from the isotropic muonium state (Mu) to the [111] axially symmetric anomalous muonium state (Mu*) in diamond. Amplitude measurements for Mu* in a powder in zero field and with a single crystal oriented in a magnetic field indicate that such a transition occurs with a temperature-dependent rateΛ(T) and that the electron polarization is conserved during the transition. The possibility of determining the absolute sign of the Mu* hyperfine parameters is discussed.