Muonium Formation in Noble Gases and Noble-Gas Mixtures

In an experiment at the Clinton P. Anderson Meson Physics Facility, no muonium formation was found in pure He or Ne, and abundant formation in Ar and Xe. A small Xe admixture (0.1%) in He and Ne resulted in abundant muonium formation, due to the process in which Xe serves as an electron donor to a low-energy positive muon. These results are qualitatively consistent with our knowledge of relevant atomic collision cross sections.