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 ± 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.

Measurement of Muonium Emission from Silica Aerogel

“…This requirement translates into the need for an ultra-slow muon source. Silica powders is known as an efficient muonium emitter in vacuum [7][8][9][10][11][12]. A major difficulty for the application of laser resonant ionization technique is that powders are not self standing.…”

Ultra slow muon source for new muon g-2 experiment

“…It is expected that muonium is formed inside silica powder particles [20] and is easily emitted from the fine particles [21] since the nominal particle radius is as small as 3.5 nm. The muonium diffuses through the voids between particles at thermal speeds and can migrate to the surface of the layer and escape the surface with significant probability [17,18,19].…”

“…The production of muonium in vacuum from silica powder was actively studied in the 1980s [17,18,19]. It is expected that muonium is formed inside silica powder particles [20] and is easily emitted from the fine particles [21] since the nominal particle radius is as small as 3.5 nm.…”

The muonium atom as a probe of physics beyond the standard model

“…[37]. With a more complete understanding of the behaviour of muonium atoms inside of a powder target a reanalysis of the data limited the coupling constant G MM to less than 20 GF (95% C.L) [38].…”

“…The observation of a few percent of the muonium atoms leaving SiO2 powder target surfaces with thermal energies at TRIUMF [38] and at at the Paul Scherrer Institut (PSI) in Villigen, Switzerland [39], was a major breakthrough in the mid 80's. It has boosted experimental efforts searching for muonium to antimuonium conversion and has been employed in all new approaches since.…”