Emission of Muonium into Vacuum from a Silica-Powder Layer

Abstract

Muonium atoms have been observed in vacuum after emission from a layer of finely divided silica powder. By extrapolation of the decay-positron track, both the time and position of muon decay are measured, confirming thermal emission at room temperature. The yields range up to (19 \ifmmode\pm\else\textpm\fi{} 6)% of muons stopping in the layer, depending on its thickness. The result is used to recalculate the upper limit for conversion of muonium to antimuonium.