Elastic Muon-Carbon Scattering in a Low-Momentum-Transfer Region

Elastic scattering of $190-\frac{\mathrm{MeV}}{c}$ muons has been measured to ∼1% in the angular range $140 \mathrm{mrad}\le \theta \le 590 \mathrm{mrad}$ corresponding to invariant four-momentum transfers $0.016 {\mathrm{fm}}^{-2\mathrm{}}\le q^2\le 0.33 {\mathrm{fm}}^{-2\mathrm{}}$. Magnetostrictive wire spark chambers were used to measure the incident momentum and scattering angle. A comparison is made with electron scattering experiments which extend down in $q^2$ to 0.02 ${\mathrm{fm}}^{-2\mathrm{}}$. A change of slope of the carbon form factor in the range below 0.05 ${\mathrm{fm}}^{-2\mathrm{}}$ would indicate unexpected structure in the outer regions of the nuclear charge distribution. Disagreement with electron scattering where both processes are measured would indicate a breakdown of muon-electron universality. No such effects are observed.