Muon-Proton Elastic Scattering at High Momentum Transfers

We have measured the muon-proton elastic scattering cross section $\frac{d\ensuremath{\sigma}}{d{q}^{2}}$ for momentum transfers in the range $10 {\mathrm{F}}^{\ensuremath{-}2}<{q}^{2}<31 {\mathrm{F}}^{\ensuremath{-}2}$ using a broad-spectrum muon beam of momenta between 1.5 and 6.0 $\frac{\mathrm{BeV}}{c}$. The muons were incident upon a large hydrogen target surrounded by an array of spark chambers and scintillation counters. We have compared our results with the equivalent electron-proton cross section to obtain a limit on the electromagnetic muon-electron difference. Assuming a lepton-vertex form factor of the type $f({q}^{2})={(1+\frac{{q}^{2}}{{\ensuremath{\Lambda}}^{2}})}^{\ensuremath{-}1}$, and defining the muon-electron difference parameter ${D}^{2}$ by $\frac{1}{{D}^{2}}=\frac{1}{\ensuremath{\Lambda}_{\ensuremath{\mu}}^{}{}_{}{}^{2}}\ensuremath{-}\frac{1}{\ensuremath{\Lambda}_{e}^{}{}_{}{}^{2}}$, we find for the 95% confidence limit ${D}^{2}>~107$ ${\mathrm{F}}^{\ensuremath{-}2}$ (${D}^{\ensuremath{-}1}<~0.09$ F; $D>~2.04 \frac{\mathrm{BeV}}{c}$).