Evidence of muonium formation using thin gold foils in vacuum

The production of thermal muonium in a vacuum region has been investigated using an array of 200 thin (∼1000 Å thick) gold foils exposed to a stopping ${\mu }^{+}$ beam. By examining the observed time dependence of the ${\mu }^{+}$-decay spectra in various transverse magnetic fields, we estimate that the lower limit of the probability of muonium formation by these gold foils placed in vacuum was 0.28±0.05.