Controlling excited-state contributions with distillation in lattice QCD calculations of nucleon isovector charges gSu−d , gAu−d , gTu−d

We investigate the application of the distillation smearing approach, and the use of the variational method with an extended basis of operators facilitated by this approach, on the calculation of the nucleon isovector charges gSu−d, gAu−d, and gTu−d. We find that the better sampling of the lattice enabled through the use of distillation yields a substantial reduction in the statistical uncertainty in comparison with the use of alternative smearing methods, and furthermore, appears to offer better control over the contribution of excited states compared to use of a single, local interpolating operator. The additional benefit arising through the use of the variational method in the distillation approach is less dramatic, but nevertheless significant given that it requires no additional Dirac inversions. Dependence of our results on the rank of the distillation is space is also explored, and found to be mild.