Scattering of High-Energy Muons on Electrons

The elastic muon-electron interactions of 10.1-GeV/c positive and 5.0- and 14.5-GeV/c negative muons produced at the Brookhaven alternating gradient synchrotron have been studied in nuclear emulsions. Energies of knockon electrons calculated from scattering measurements were compared with those obtained from their ejection angles. Integral cross sections were compared with the Bhabha prediction for the scattering of two point fermions. Excellent agreement was found for negative and positive primary muons up to $t=3.3\mathrm{}\times {10}^{-3\mathrm{}}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ and $t=1.8\mathrm{}\times {10}^{-3\mathrm{}}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$, respectively. Our results are in contradiction to some of the previous cosmic-ray data, which show an anomalously large cross section.