Comparison of Muon-Proton and Electron-Proton Inelastic Scattering

Measurements of the differential cross section for the inelastic scattering of 12-GeV/c muons on protons are reported. These measurements cover a kinematic range of $\left|q^2\right|$ (the square of the four-momentum transferred from the lepton) up to 4.0 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ and of muon energy losses ($\nu$) up to 9.0 GeV. Only the scattered muon is observed in an optical spark-chamber apparatus. The data are compared with electron-proton inelastic scattering, and analyzed in terms of possible lepton form factors and anomalous interactions. $\mu -p$ inelastic scattering is found to exhibit the same mild $\left|q^2\right|$ behavior as does $e-p$ inelastic scattering. No experimentally significant deviation from the predictions of muon-electron universality has been found. If the ratio of muon to electron inelastic cross sections is parametrized by the form ${(1.0+\frac{\left|q^2\right|}{\Lambda _D^{}{}_{}{}^2})}^{-2\mathrm{}}$, we find with 97.7% confidence that ${\Lambda }_D>4.1\mathrm{}$ GeV/c. The muon-proton cross sections on the average are slightly smaller than the electron-proton cross sections. This observation is not experimentally significant because such a difference might be caused by systematic errors, but this observation is used to speculate as to the most fruitful direction for future experiments.