First observation of spin flip in d mu-atoms via formation and back decay of dd mu molecules

We present the results of precision measurements of d mu spin-flip rates in pure D-2, in pure HD gas, and in the non-equilibrium and equilibrium H-2 D-2 gas mixtures. The experiments were performed at PSI in 1994-1996 using the high pressure ionization chamber from Gatchina as a 100\% efficient de tector of the charged fusion products. The measurements have been carried o ut in the temperature range 28-300 K, at gas density of 5% of LHD. In pure deuterium, the measured temperature dependence of the spin-flip rate allowe d us to separate the two components (resonant and non-resonant) of the spin -flip processes. From the experiments in H/D mixtures we have measured the non-resonant spin-flip rate in collisions of d mu-atoms with HD molecules. Comparison with the theory revealed considerable disagreement in the case o f non-resonant spin-flip in collisions of the d mu-atoms with D-2 molecules .