Dependence of muon-catalyzed d-d fusion on the ortho-para ratio in solid and liquid deuterium

The effect of the ortho-para ratio on muon-catalyzed d-d fusion reactions in solid and liquid deuterium at 5.5-23.2 K has been investigated. An unexpected decrease in the resonant ddμ molecular formation rate and in the dμ hyperfine transition rate has been clearly observed in liquid ortho-rich deuterium as well as the solid form. The result in the liquid phase does not agree with theoretical predictions for isolated D2 molecules. This fact indicates that the resonance condition in the solid and liquid phases differs from theoretical predictions presumably due to a high-density condensed-matter effect common to liquids and solids. The dμ hyperfine transition rate via back-decay, the dμ hyperfine-transition rate via scattering, and the back-decay rate have also been directly determined in the solid and liquid phases.