Hadronic effects in parity violating electron scattering

Date of Completion

January 2004


Physics, Nuclear|Physics, Elementary Particles and High Energy




Since their advent, Parity Violating experiments have played a crucial role in testing the standard model (SM) of electroweak interactions. In recent years, these experiments have reached such a high degree of accuracy that they might test for physics beyond the SM. When making high precision measurements, a recurrent problem is how to properly include hadronic corrections. In this study I consider possible hadronic effects that appear in such experiments. ^ In the first part, I consider the possible hadronic corrections to the deep inelastic parity violating asymmetry (PVA), stemming from sea quarks, perturbative QCD, target mass and higher twist (HT) corrections. To estimate the first three effects I use available parameterizations of the leading twist parton distribution functions. For the HT, I suggest using the MIT bag model to give some reasonable estimate. ^ In the second part I study the contribution to the PVA of the bremsstrahlung radiation in electron-proton scattering. This process constitutes a background in the SLAC experiment E-158. In the experiment, which uses polarized Møller scattering to measure the PVA at the 8% level, it was noticed that the inelastic electron-proton (EP) scattering background amounted for 40% of the total asymmetry, which implies that one has to know the EP background to a 20% level. I suggest to use a simple two resonances model to investigate which fraction of the bremmstrahlung radiation in the proton electro-excitation contributes to the total background and if the lack of knowledge in the resonance form factors might spoil the prescribed accuracy of the experiment. ^ In the last part of the study I estimate the contribution to the PVA in the electro-excitation of the Δ(1232) resonance in chiral perturbation theory. I focus on the chiral corrections of the terms stemming from the electric-dipole, the anapole and the d-wave chiral effective lagrangian and give some reasonable range of values for their contribution to the PVA in the low Q 2 region. ^