Nucleon Charges and Electromagnetic Form Factors from 2+1+1-Flavor Lattice QCD

TL;DR

This paper presents lattice-QCD calculations of nucleon charges and form factors, emphasizing the importance of accounting for excited-state contamination to obtain accurate results.

Contribution

It provides high-statistics lattice-QCD results for nucleon properties using multiple source-sink separations and systematic excited-state analysis.

Findings

Including excited states reduces systematic errors.

Multiple source-sink separations are essential for accurate matrix elements.

Results are consistent with previous lattice calculations.

Abstract

We present lattice-QCD results on the nucleon isovector axial, scalar and tensor charges, the isovector electromagnetic Dirac and Pauli form factors, and the connected parts of the isoscalar charges. The calculations have been done using two ensembles of HISQ lattices generated by the MILC Collaboration with 2+1+1 dynamical flavors at a lattice spacing of 0.12 fm and with light-quark masses corresponding to pions with masses 310 and 220 MeV. We perform a systematic study including excited-state degrees of freedom and examine the dependence of the extracted nucleon matrix elements on source-sink separation. This study demonstrates with high-statistics data that including excited-state contributions and generating data at multiple separations is necessary to remove contamination that would otherwise lead to systematic error. We also determine the renormalization constants of the associated quark bilinear operators in the RI-sMOM scheme and make comparisons of our renormalized results with previous dynamical-lattice calculations.