Two-boson exchange corrections to parity-violating elastic electron-proton scattering

摘要

Details of the calculation of two-boson exchange effects in parity-violating elastic ep scattering within a simple hadronic model, including both the nucleon and the Δ(1232)-resonance intermediate states, are presented. We examine the sensitivity of our results with respect to choice of form factors. We emphasize the importance of using correct relations relating N→Δ and Δ→N transition vertex functions. The NΔ Coulomb quadrupole transition is found to play an important role at higher Q2⩾3.0 GeV2. We also elucidate the relation between our results and the well-known result on the γZ-boson exchange effect given by Marciano and Sirlin. The effect of the nucleon contribution δN to parity asymmetry APV is found to be, in general, larger than the corresponding Δ contribution δΔ except at extreme forward angles. Corrections to the extracted values of the strange form factors GEs+βGMs from the HAPPEX, A4, and G0 data are also presented. The total TBE corrections to the extracted values of GEs+βGMs in recent HAPPEX, G0, and A4 experiments are, depending on kinematics, found to be small except in a few cases where they range from -20.6% to 48.3%.