Muon transfer from hydrogen to argon and helium at 10<i>–</i>15 bars

The transfer of negative muons from the ground state of muonic hydrogen to argon and helium has been measured in gaseous mixtures at pressures between 10 and 15 bars and at different relative concentrations. The transfer rate to argon, reduced to liquid-hydrogen density [${\ensuremath{\Lambda}}_{p\mathrm{Ar}}$ =1.42(4)\ifmmode\times\else\texttimes\fi{}${10}^{11}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$], agrees well with those obtained at ten times higher pressures. The transfer rate to helium [${\ensuremath{\Lambda}}_{p\mathrm{He}=0.88(9)\ifmmode\times\else\texttimes\fi{}{10}^{8}}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$], measured in a triple gas mixture, disagrees with the only other experimental value and is about two times higher than recent theoretical predictions. In addition, the muonic x-ray intensities of the Lyman series of argon resulting from muon transfer have been determined. They are well reproduced by a cascade calculation assuming a theoretical initial distribution over n and l states.