Scattering of High-Energy Positive and Negative Muons on Electrons

A counter experiment on ${\mu }^{\pm }e$ scattering has been performed in the muon beam at the Brookhaven AGS with particular emphasis on a possible asymmetry. Two strongly filtered beams of either sign were available, one peaked at 10.5 GeV/c, and the other at 5.5 GeV/c produced by further energy degradation in a uranium absorber. Electron energies were measured in terms of the light output produced by the cascade shower generated in a total absorption multilayer Pb scintillator counter. Two types of runs were made using the same apparatus with different event selection. In the first type all incident muons triggering the beam-defining hodoscope were counted, the effective target was distributed through the entire apparatus, and all pulses from the shower counter were measured and stored in a 400-channel pulse-height analyzer. In the second type the target volume was rather well defined, by a suitable pulse signature, to be the middle one of three water-Čerenkov counters placed in tandem in front of the shower detector. Results of the first type show that there is no asymmetry >±10% in the total electromagnetic energy loss spectrum from 0.1 to 6 GeV. Results of the second type, which have less good statistics, give the absolute $\mu -e$ scattering cross section to ±30% with no indication of an asymmetry.