We present updated results for the nucleon axial charge and electromagnetic (EM) form factors, which include a significant increase in statistics for all ensembles (up to 4000 measurements), as well as the addition of ensembles with pion masses down to $m_\pi\sim195$ MeV. We also present results for the average quark momentum fraction. The new data allows us to perform a thorough study of the systematic effects encountered in the lattice extraction. We concentrate on systematic effects due to excited-state contaminations for each of the quantities, which we check using several different time separations between the operators at the source and sink through a comparison of plateau fits and the summed operator insertion method (which provides a mechanism to suppress the excited-state contamination). We confirm our earlier finding that a reliable extraction of the axial charge must be based on a method which eliminates excited-state contaminations. Similar conclusions apply to our EM form factor calculations . The measurements are calculated using the CLS ensembles with non-perturbatively O(a) improved Wilson fermions in $N_f=2$ QCD.
|Journal||P o S - Proceedings of Science|
|Number of pages||13|
|Publication status||Published - 22. Nov 2013|
|Event||31st International Symposium on Lattice Field Theory LATTICE 2013: LATTICE 2013 - Mainz, Germany|
Duration: 29. Jul 2013 → 3. Aug 2013
|Conference||31st International Symposium on Lattice Field Theory LATTICE 2013|
|Period||29/07/2013 → 03/08/2013|