Observation of Muonium in Vacuum

Abstract

The first observation of muonium (${\mu }^{+}{e}^{-}$) in vacuum, produced when a low-energy positive muon beam impinges on a thin foil target, is reported. It is found that ${\mu }^{+}{e}^{-}$ emerges from the foil surface predominantly with energies of less than 20 keV. The results show that the Clinton P. Anderson Meson Physics Facility stopped-muon channel operating at $E=4.0\mathrm{}$ MeV with an average flux of 3×${10}^6$ ${\mathrm{\mu }}^{+}$/s can produce roughly ${10}^3$ ${\mathrm{\mu }}^{+}$ ${\mathrm{e}}^{-}$/s in vacuum from thin targets of Be, C, Al, Cu, Ag, and Au.