Room-temperature emission of muonium from aerogel and zeolite targets

Abstract

Novel emitters of muonium ($\mathrm{Mu}={\ensuremath{\mu}}^{+}+{e}^{\ensuremath{-}}$) with high conversion efficiencies can enhance the precision of muonium spectroscopy experiments and enable next-generation searches for new physics. At the Paul Scherrer Institute (PSI), we investigate muonium production at room-temperature as well as in cryogenic environment using a superfluid helium converter. In this paper, we describe the development of compact detection schemes which resulted in the background-suppressed observation of atomic muonium in vacuum, and can be adapted for cryogenic measurements. Using these setups, we compared the emission characteristics of various muonium production targets at room temperature using low momentum (${p}_{\ensuremath{\mu}}=11--13\phantom{\rule{4pt}{0ex}}\mathrm{MeV}/c$) muons, and observed muonium emission from zeolite targets into vacuum. For a specific laser-ablated aerogel target, we determined a muon-to-vacuum-muonium conversion efficiency of $7.23\ifmmode\pm\else\textpm\fi{}0.05{\text{(stat)}}_{\ensuremath{-}0.76}^{+1.06}\text{(sys)}\phantom{\rule{0.16em}{0ex}}%$, assuming thermal emission of muonium. Moreover, we investigated muonium-helium collisions and from it we determined an upper temperature limit of 0.3 K for the superfluid helium converter.