Nucleon axial, scalar, and tensor charges using lattice QCD at the physical pion mass

Abstract

We report on lattice QCD calculations of the nucleon isovector axial, scalar, and tensor charges. Our calculations are performed on two $2+1$-flavor ensembles generated using a 2-HEX-smeared Wilson-clover action at the physical pion mass and lattice spacings $a\ensuremath{\approx}0.116$ and 0.093 fm. We use a wide range of source-sink separations---eight values ranging from roughly 0.4 to 1.4 fm on the coarse ensemble and three values from 0.9 to 1.5 fm on the fine ensemble---which allows us to perform an extensive study of excited-state effects using different analysis and fit strategies. To determine the renormalization factors, we use the nonperturbative Rome-Southampton approach and compare ${\mathrm{RI}}^{\ensuremath{'}}\text{\ensuremath{-}}\mathrm{MOM}$ and RI-SMOM intermediate schemes to estimate the systematic uncertainties. Our final results are computed in the $\overline{\mathrm{MS}}$ scheme at scale 2 GeV. The tensor and axial charges have uncertainties of roughly 4%, ${g}_{T}=0.972(41)$ and ${g}_{A}=1.265(49)$. The resulting scalar charge, ${g}_{S}=0.927(303)$, has a much larger uncertainty due to a stronger dependence on the choice of intermediate renormalization scheme and on the lattice spacing.