Ground-state muon transfer from deuterium to ^{3}He and ^{4}He

We have observed the deexcitation x-ray spectra of the exotic molecules (d mu(4)He)* and (d mu(3)He)* with good statistics and low background. From the time distributions of these x rays, we have directly determined the muon transfer rates from ground-state muonic deuterium atoms to helium nuclei. The obtained transfer rates in gaseous mixtures at similar to 30 K are lambda(d3He) = (1.856+/-0.077) x 10(8) s(-1) to He-3, and lambda(d4He) = (10.50+/-0.21) x 10(8) s(-1) to He-4. In liquid mixtures, we measured the muon transfer rates lambda(d3He) = (2.17+/-0.73) x 10(8) s(-1) and lambda(d4He) = (13.2+/-1.3) x 10(8) s(-1). These transfer rates have to be multiplied with the target density and the atomic helium concentration to obtain the "effective transfer rates" for a specific target composition. The expected isotopic effect between mixtures containing He-3 and mixtures containing He-4, as well as with respect to the hydrogen-helium case, is clearly confirmed. A density effect was observed for both isotopic compositions. We investigated the widths and the energies of the intensity maxima of the observed energy spectra of the molecular x rays. From the comparison of the measured energy spectra with calculated ones, we conclude that decay from the rotational state J = 1 of the muonic molecule dominates over decay from J = 0 at the investigated experimental conditions.