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.
|Tidsskrift||P o S - Proceedings of Science|
|Status||Udgivet - 22. nov. 2013|
|Begivenhed||31st International Symposium on Lattice Field Theory LATTICE 2013: LATTICE 2013 - Mainz, Tyskland|
Varighed: 29. jul. 2013 → 3. aug. 2013
|Konference||31st International Symposium on Lattice Field Theory LATTICE 2013|
|Periode||29/07/2013 → 03/08/2013|
Bibliografisk note13 pages, 7 figures; talk presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, Germany; typos corrected, plots relabelled, conclusions unchanged