Ground-state muon transfer from deuterium to3Heand4He

Abstract

We have observed the deexcitation x-ray spectra of the exotic molecules $(d{\ensuremath{\mu}}^{4}\mathrm{He}{)}^{*}$ and $(d{\ensuremath{\mu}}^{3}\mathrm{He}{)}^{*}$ 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 $\ensuremath{\sim}30$ K are ${\ensuremath{\lambda}}_{{d}^{3}\mathrm{He}}=(1.856\ifmmode\pm\else\textpm\fi{}0.077)\ifmmode\times\else\texttimes\fi{}{10}^{8} {\mathrm{s}}^{\ensuremath{-}1}$ to ${}^{3}\mathrm{He},$ and ${\ensuremath{\lambda}}_{{d}^{4}\mathrm{He}}=(10.50\ifmmode\pm\else\textpm\fi{}0.21)\ifmmode\times\else\texttimes\fi{}{10}^{8} {\mathrm{s}}^{\ensuremath{-}1}$ to ${}^{4}\mathrm{He}.$ In liquid mixtures, we measured the muon transfer rates ${\ensuremath{\lambda}}_{{d}^{3}\mathrm{He}}=(2.77\ifmmode\pm\else\textpm\fi{}0.73)\ifmmode\times\else\texttimes\fi{}{10}^{8} {\mathrm{s}}^{\ensuremath{-}1}$ and ${\ensuremath{\lambda}}_{{d}^{4}\mathrm{He}}=(14.2\ifmmode\pm\else\textpm\fi{}1.4)\ifmmode\times\else\texttimes\fi{}{10}^{8} {\mathrm{s}}^{\ensuremath{-}1}.$ 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 ${}^{3}\mathrm{He}$ and mixtures containing ${}^{4}\mathrm{He},$ 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.