We report on our calculation of the nucleon axial charge $g_{\mathrm{A}}$ in QCD with two flavors of dynamical quarks. A detailed investigation of systematic errors is performed, with a particular focus on contributions from excited states to three-point correlation functions. The use of summed operator insertions allows for a much better control over such contamination. After performing a chiral extrapolation to the physical pion mass, we find $g_{\mathrm{A}}=1.223\pm 0.063(\mathrm{stat}{)}_{-0.060}^{+0.035}(\mathrm{syst})$, in good agreement with the experimental value.

• Received 4 May 2012

DOI:https://doi.org/10.1103/PhysRevD.86.074502