QED+QCD Corrections to the Anomalous Magnetic Moment of the Muon

Abstract

The current 3:7 discrepancy between experimental and Standard Model determinations of the anomalous magnetic moment has long stood without resolution. This serves as an important test for the Standard Model of particle physics, which is the best theory we have to describe the universe at a subatomic scale. If this discrepancy can be removed though an increase of the precision of the experimental results and Standard Model calculations, we will have another important constraint on the Standard Model. On the other hand, if this discrepancy is increased we will have important evidence of new physics effects, beyond our current understanding. Either resolution will be of great impact for the physics community. The large majority of the Standard Model uncertainty comes from hadronic contributions. In this thesis we investigate improvements to the leading order hadronic contribution using a technique called lattice gauge theory. In particular, we will look at the inclusion of QED corrections to the leading order hadronic contribution using fully dynamical QCD+QED gauge eld ensembles generated by the QCDSF collaboration. This investigation is undertaken using two lattice volumes, with three sets of sub-ensembles on each volume. In order to extrapolate the results to the physical quark mass we also use a range of partially quenched quark masses, corresponding to pion masses ranging from 230 MeV to 790 MeV. From this study we find the QED corrections to be 0:2% 0:1%. While small, this is in no way insignificant. Current lattice studies aim for a precision greater than 0:5%, making the QED corrections of great importance in meeting that goal. We also present an exploratory investigation into the QED corrections to the leading order disconnected contribution. This is done at the SU(3) symmetric point using a single lattice volume. We find a QED correction of O(0:5%).