We report on an experiment at the Paul Scherrer Institute, Villigen, Switzerland measuring x rays from muon transfer from deuterium to helium. Both the ground-state transfer via the exotic $(d{\mu }^{3,4}\mathrm{He}{)}^{*}$ molecules and the excited-state transfer from $(\mu {d)}^{*}$ were measured. The use of charge-coupled device detectors allowed x rays from 1.5 keV to 11 keV to be detected with sufficient energy resolution to separate the transitions to different final states in both deuterium and helium. The x-ray peaks of the $(d{\mu }^3\mathrm{He}{)}^{*}$ and $(d{\mu }^4\mathrm{He}{)}^{*}$ molecules were measured with good statistics. For the ${\mathrm{D}}_2{+}^3\mathrm{He}$ mixture, the peak has its maximum at $E_{d{\mu }^3\mathrm{He}}=6768\mathrm{}\pm 12\mathrm{eV}$ with full width at half maximum (FWHM) ${\Gamma }_{d{\mu }^3\mathrm{He}}=863\mathrm{}\pm 10\mathrm{eV}.$ Furthermore, the radiative branching ratio was found to be ${\kappa }_{d{\mu }^3\mathrm{He}}=0.301\mathrm{}\pm \mathrm{0.061.}$ For the ${\mathrm{D}}_2{+}^4\mathrm{He}$ mixture, the maximum of the peak lies at $E_{d{\mu }^4\mathrm{He}}=6831\mathrm{}\pm 8\mathrm{eV}$ and the FWHM is ${\Gamma }_{d{\mu }^4\mathrm{He}}=856\mathrm{}\pm 10\mathrm{eV}.$ The radiative branching ratio is ${\kappa }_{d{\mu }^4\mathrm{He}}=0.636\mathrm{}\pm \mathrm{0.097.}$ The excited-state transfer is limited by the probability to reach the deuterium ground state, $q_{1s}.$ This coefficient was determined for both mixtures: $q_{1s}^{{}^3\mathrm{He}}=68.9\mathrm{}\pm 2.7$% and $q_{1s}^{{}^4\mathrm{He}}=90.1\mathrm{}\pm 1.5\%.$

• Received 19 February 2003

DOI:https://doi.org/10.1103/PhysRevA.68.022712