Muon-Proton Elastic Scattering at High Momentum Transfers

We have measured the muon-proton elastic scattering cross section dσdq² for momentum transfers in the range 10 F^-2<q²<31 F^-2 using a broad-spectrum muon beam of momenta between 1.5 and 6.0 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(q²)=(1+q²Λ²)^-1, and defining the muon-electron difference parameter D² by 1D²=1Λ_μ^_²-1Λₑ^_², we find for the 95% confidence limit D²>~107 F^-2 (D^-1<~0.09 F; D>~2.04 BeV/c).