Isovector charges of the nucleon from 2+1-flavor QCD with clover fermions

TL;DR

This study provides high-precision lattice QCD estimates of the nucleon's isovector charges using advanced computational techniques and multiple ensembles, demonstrating control over excited-state contamination and consistency with other formulations.

Contribution

It introduces a multistate analysis approach for nucleon charge calculations with high statistics and demonstrates agreement across different lattice formulations.

Findings

Accurate estimates of $g_A$, $g_S$, and $g_T$ charges.

Effective control of excited-state contamination.

Consistency with previous lattice results.

Abstract

We present high-statistics estimates of the isovector charges of the nucleon from four 2+1-flavor ensembles generated using Wilson-clover fermions with stout smearing and tree-level tadpole improved Symanzik gauge action at lattice spacings $a=0.114$ and $0.080$ fm and with $M_\pi \approx 315$ and 200 MeV. The truncated solver method with bias correction and the coherent source sequential propagator construction are used to cost-effectively achieve $O(10^5)$ measurements on each ensemble. Using these data, the analysis of two-point correlation functions is extended to include four states in the fits and of three-point functions to three states. Control over excited-state contamination in the calculation of the nucleon mass, the mass gaps between excited states, and in the matrix elements is demonstrated by the consistency of estimates using this multistate analysis of the spectral decomposition of the correlation functions and from simulations of the three-point functions at multiple values of the source-sink separation. The results for all three charges, $g_A$, $g_S$ and $g_T$, are in good agreement with calculations done using the clover-on-HISQ lattice formulation with similar values of the lattice parameters.