Abstract
We report on an analysis of the average quark momentum fraction of the nucleon and related quantities using Nf = 2 + 1 Wilson fermions. Computations are performed on four CLS ensembles covering three values of the lattice spacing at pion masses down to Mπ ≈ 200 MeV. Several source-sink separations (~ 1:0 fm to ~ 1:4 fm) are used to assess the excited-state contamination. To gain further insight, the generalized pencil-of-functions approach has been implemented to reduce the excited-state contamination in the relevant two-and three-point functions. Preliminary results are shown for the isovector nucleon charges from vector, axial vector and tensor derivative (twist-2) operators.
Highlights
In this proceedings contribution we present a nucleon structure calculation by the Mainz group concerning twist-2 operator insertions with focus on the nucleon quark momentum fraction
The resulting statistical error is typically larger than for the plateau method. Another way to tackle the excited-state problem is the so-called generalized pencil-of-function (GPOF) approach, which was first applied for baryon calculations in a study of the electromagnetic form factor of the ∆ [10, 11]
We have included the data for the corresponding ratios from the GPOF approach in Eq (15), where the three lower values of tsep have been used in the operator construction
Summary
In this proceedings contribution we present a nucleon structure calculation by the Mainz group concerning twist-2 operator insertions with focus on the nucleon quark momentum fraction. It is complementing a similar study of local charges and electromagnetic form factors which has been presented at this conference [1]. The nucleon quark momentum fraction is defined as the first momentum of the distribution of unpolarized quarks x q = dx x · q(x) + q(x). One defines the first moment helicity and transversity moments x ∆q and x δq from distributions of correspondingly polarized quarks ∆q and δq. In lattice QCD, suitable twist-2 operator insertions for nucleon three-point functions are required to compute these observables
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