Mass and isovector matrix elements of the nucleon at zero-momentum transfer

TL;DR

This paper reports on lattice QCD calculations of nucleon structure observables, including isovector charges, twist-2 matrix elements, and nucleon mass, using extensive ensembles to improve accuracy and control excited-state contamination.

Contribution

It provides updated results with finer lattice spacing, larger volumes, and improved analysis techniques for nucleon matrix elements compared to previous studies.

Findings

Results include isovector charges and twist-2 matrix elements.

Enhanced control over excited-state contamination.

Data at very fine lattice spacing and large volume.

Abstract

We present the current status of our analysis of nucleon structure observables including isovector charges and twist-2 matrix elements as well as the nucleon mass. Results are computed on a large set of CLS $N_f=2+1$ gauge ensembles with $M_\pi\approx0.130\mathrm{MeV}\ldots 350\mathrm{MeV}$, four values of the lattice spacing $a=0.05\mathrm{fm}\ldots 0.09\mathrm{fm}$ and covering a large range of physical volumes. Compared to the results presented at last year's conference we have added data on a very fine and large box at small light quark mass ($T\times L^3=192 \times 96^3$, $M_\pi=172\mathrm{MeV}$, $a=0.05\mathrm{fm}$). Additional (intermediate) source-sink separations have been computed on the coarser ensembles, further increasing effective statistics and allowing for a more fine-grained control in the treatment of the excited-state contamination. Excited states in the nucleon matrix elements are tamed by a simultaneous, two-state fit ansatz using the summation method.