Muon-Proton Elastic Scattering at High Momentum Transfers

We have measured the muon-proton elastic scattering cross section $\frac{d\sigma }{d{q}^2}$ for momentum transfers in the range $10 {\mathrm{F}}^{-2\mathrm{}}<q^2<31\mathrm{} {\mathrm{F}}^{-2\mathrm{}}$ 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 $f\left(q^2\right)={(1+\frac{q^2}{{\Lambda }^2})}^{-1\mathrm{}}$, and defining the muon-electron difference parameter $D^2$ by $\frac{1}{D^2}=\frac{1}{\Lambda _{\mu }^{}{}_{}{}^2}-\frac{1}{\Lambda _e^{}{}_{}{}^2}$, we find for the 95% confidence limit $D^2>~107$ ${\mathrm{F}}^{-2\mathrm{}}$ ($D^{-1\mathrm{}}<~0.09$ F; $D>~2.04 \frac{\mathrm{BeV}}{c}$).