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An improved upper limit for muonium conversion to antimuonium Marshall, Glen Murray


An experiment resulting in the reduction of the upper limit for muonium (µ+e⁻) conversion to antimuonium (µ⁻e*) is described. The limit obtained for the effective four fermion coupling constant is G < 42GF (95% confidence level). The muon in a system initially formed as muonium and evolving under the most favorable conditions will thus be identifiable as a negative particle in less than 4% of the observed decays. The results improve by over one order of magnitude the best previous limit obtained from a search for e⁻e⁻ ->µ⁻µ⁻ interactions. Neither process is expected to exist if an additive conservation law is obeyed by muon number. The present status of the theory of electroweak interactions, as it pertains to muonium conversion, is reviewed. It is shown that muon number noncohservation can be accommodated in a variety of ways, some of which might allow a value for G of 0.1GF. The steps that were taken to make the present experiment as sensitive as possible are detailed. The major improvement over previous conversion experiments is the use of fine silica powder in carefully arranged layers to allow muonium to exist for a large fraction of its lifetime in vacuum, where conversion is not highly suppressed. Another important facet of the technique, which is described in detail, is the use of an intense beam of surface muons with a stopping density previously unattainable. A chapter on the analysis of the data contains a quantitative discussion of the processes which must occur for conversion to be detected. The numbers derived there are essential to the establishment of a realistic limit on the coupling of muonium to antimuonium.

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