Precision study of excited state effects in nucleon matrix elements

Abstract: We present a dedicated analysis of the influence of excited states on the calculation of nucleon matrix elements. This calculation is performed at a fixed value of the lattice spacing, volume and pion mass that are typical of contemporary lattice computations. We focus on the nucleon axial charge, , for which we use about 7500 measurements, and on the average momentum of the unpolarized isovector parton distribution, , for which we use about measurements. All computations are done employing maximally-twisted-mass Wilson fermions and using non-perturbatively calculated renormalization factors. Excited state effects are shown to be negligible for , whereas they lead to an downward shift for . [Copyright &y& Elsevier]