Electromagnetic radiative corrections in parity-violating electron-proton scattering

Abstract

QED radiative corrections have been calculated for leptonic and hadronic variables in parityviolating elastic ep scattering. For the first time, the calculation of the asymmetry in the elastic radiative tail is performed without the peaking-approximation assumption in hadronic variables configuration. A comparison with the PV-A4 data validates our approach. This method has been also used to evaluate the radiative corrections to the parity-violating asymmetry measured in the G0 experiment. The results obtained are here presented.PACS. 25.30.Bf Elastic electron scattering -13.60.-r Photon and charged-lepton interactions with hadrons

Measurement of the strange quark contribution to the vector structure of the proton

“…Following the increase in Q 2 , the effect is that the radiative corrections increase the average asymmetry. The increase is of order 0.5-3.0% over the range of the detectors [81].…”

“…Although the first-order electromagnetic and neutral weak interactions are the processes of interest (and are the dominant ones), important higher-order electroweak processes do contribute to electroweak-nucleon scattering, and so there must be corrections made to account for them [81][82][83].…”

“…This has the consequence of increasing the magnitude of the measured elastic asymmetry from the anticipated Born asymmetry. A dedicated CEANT simulation was developed to treat the radiative corrections for C 0 [81,272,273]. Four types of radiative corrections were considered for the measurement: ionization, external, internal real and internal virtual radiative corrections.…”

“…In principle, the electrons in the beam can lose all their energy through radiation. However, the probability that they lose 500 MeV or less is about 96%, and only about 60% of the electrons lose 1 keV or less [81]. The 4% of electrons that lose more than 500 MeV correspond to protons that have times-of-flight outside of the G 0 experimental cuts, and are therefore ignored.…”

“…In addition, another estimate of the uncertainty was done by making a global fit of the ratio Ae~/ARc with a polynomial and assuming that the difference with the actual RC correction is due to systematics. The uncertainty varies slowly and is of the order 0.1-0.3%, about 10% of the actual correction, depending on the detector bin [81,272]. The correction was applied as an overall multiplicative factor, Aphys(Q 2 ) = R x Ae, which gives back the Born asymmetry to be compared to theory.…”