Sign of the hyperfine parameters of anomalous muonium in diamond

Observations with the muon-spin-rotation (μSR) technique of the thermally activated transition from the isotropic muonium state Mu to the anisotropic muonium state ${\mathrm{Mu}}^{\mathrm{*}}$ in diamond are used to determine the sign of the ${\mathrm{Mu}}^{\mathrm{*}}$ hyperfine constants. It is found that the isotropic part of the ${\mathrm{Mu}}^{\mathrm{*}}$ hyperfine interaction is negative, indicating the importance of exchange polarization. The transition rate from Mu to ${\mathrm{Mu}}^{\mathrm{*}}$ follows an Arrhenius law over more than four decades. Finally, data are presented on the temperature dependence of the hyperfine interaction of isotropic Mu in diamond.