Excited State Effects in Nucleon Matrix Element Calculations

TL;DR

This paper presents a high-precision lattice QCD study of nucleon matrix elements, analyzing excited state effects using advanced methods and providing new insights into key nucleon properties like $g_A$ and $<x>_{u-d}$.

Contribution

It introduces an open sink method for exploring excited states and compares it with the generalized eigenvalue approach in nucleon matrix element calculations.

Findings

Quantified excited state contributions to nucleon matrix elements.

Provided high-precision estimates for $g_A$ and $<x>_{u-d}$.

Compared effectiveness of different analysis methods.

Abstract

We perform a high-statistics precision calculation of nucleon matrix elements using an open sink method allowing us to explore a wide range of sink-source time separations. In this way the influence of excited states of nucleon matrix elements can be studied. As particular examples we present results for the nucleon axial charge $g_A$ and for the first moment of the isovector unpolarized parton distribution $<x>_{u-d}$. In addition, we report on preliminary results using the generalized eigenvalue method for nucleon matrix elements. All calculations are performed using $N_f=2+1+1$ maximally twisted mass Wilson fermions.