HAPPEX III Instrumentation and Systematic Errors

HAPPEX III measures the parity-violating asymmetry in the elastic scattering of electrons from protons at an average $Q^2$ of $0.62GeV^2$. A linear combination of strange-quark vector form factors $G^S_E + 0.53G^S_M$ is extracted from this measurement. The corrections to this measurement and associated bounds on systematic errors are discussed in detail. Corrections include rescattering inside the spectrometers, aluminum contamination, detector non-linearities, and radiative and finite acceptance corrections in $Q^2$ measurements.