Calculation of the axial charge of a heavy nucleon in Lattice QCD

Abstract

In this thesis, we aim to calculate the non-renormalized axial charge gA of a heavy nucleon made out of quarks at the physical mass of the strange quark. We present the framework of Lattice QCD which makes the calculation of such observables attainable from first principles. The data used for the estimation of gA were obtained on a 243 x64 hypercubic lattice with lattice spacing a ~ 0.12 fm and pion mass m[pi] = 0.450 GeV. Three different source-sink seperations were used, tsink = [12a, 14a, 16a]. For each timeslice seperation signal we perform a correlated x2 fit and obtain the following values for gA: 0.551, 0.564 and 0.556. The unrenormalized value value for gA is extracted taking the limit as tsink --> [infinity] and is shown to be gA = 0.558. We discuss how the accuracy of this result is compromised by the small number of tsink values, by excited state contamination and by the increase of statistical noise with time.