F eb 2 00 9 Hadronic Effects in Parity Violating Electron Scattering

Since their advent, Parity Violating experiments have played a crucial role intesting the standard model (SM) of electroweak interactions. In recent years, these experi-ments have reached such a high degree of accuracy that they might test for physics beyondthe SM. When making high precision measurements, a recurrent problem is how to properlyinclude hadronic corrections. In this study I consider possible hadronic effects that appearin such experiments.In the first part, I consider the possible hadronic corrections to the deep inelastic parityviolating (PV) asymmetry, ARL [1], stemming from sea quarks, perturbative QCD (PQCD),target mass (TM) and higher twist (HT) corrections. To estimate the first three effectsI use available parametrizations of the leading twist parton distribution functions (PDF).For the HT, which are not well known, I suggest using the MIT bag model to give somereasonable estimate. HT corrections could be relevant at the kinematics in the proposedexperiments [2,3] where the weak mixing angle θW may be measured by using ARL. In thispart of the study I consider the implications of these corrections for the extraction of sin θW .In the second part I study the contribution to ARL of the bremsstrahlung radiation inelectron-proton scattering. Such a process constitutes a background in the SLAC experi-ment E-158. In the experiment, which uses polarized Møller scattering to measure ARL atthe 8% level, it was noticed that the inelastic electron-proton (EP) scattering backgroundamounted for 40% of the total asymmetry, which implies that, in order to reach the pre-scribed precision in the ARL, one has to know the EP background to a 20% level. I suggestto use a simple model, consisting in only two resonances, to investigate which fraction ofthe bremmstrahlung radiation in the proton electro-excitation contributes to the total back-ground and if the lack of knowledge in the resonance form factors might spoil the prescribedaccuracy of the experiment.In the last part of the study I estimate the contribution to ARL in the electro-excitationof the ∆(1232) resonance in chiral perturbation theory. I specifically focus on the chiralcorrections of the terms stemming from the electric-dipole, the anapole and the d-wave chi-ral effective lagrangian and give some reasonable range of values for their contribution toARL in the low Q2 region. In particular the dipole (or Siegert) contribution assumes greatimportance at very low Q since it does not vanish at the photon point, while all the othercontributions do.