We report the first measurement using a solid polarized target of the neutron electric form factor $G_E^n$ via $\overrightarrow{d}\left(\overrightarrow{e}{,e}^{\prime }n\right)p$. $G_E^n$ was determined from the beam-target asymmetry in the scattering of longitudinally polarized electrons from polarized deuterated ammonia ( ${}^{15}{\mathrm{ND}}_3$). The measurement was performed in Hall C at Thomas Jefferson National Accelerator Facility in quasifree kinematics with the target polarization perpendicular to the momentum transfer. The electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle segmented detector. We find $G_E^n=0.04632\mathrm{}\pm 0.00616\left(\mathrm{stat}\right)\pm 0.00341\left(\mathrm{syst}\right)$ at $Q^2=0.495\mathrm{}(\mathrm{GeV}/c{)}^2$.

• Received 26 March 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.081801