Speaker
Description
We present results for the isovector axial form factor of the nucleon computed on a set of $N_f = 2 + 1$ CLS ensembles with $\mathcal{O}(a)$-improved Wilson fermions and the Lüscher-Weisz gauge action. The set of ensembles covers a range of pion masses from 353 MeV down to the physical pion mass, and lattice spacings between 0.05 fm and 0.09 fm.
We use the summed operator insertion method (summation method) to suppress the contamination from excited states, and use the $z$-expansion to parametrise the $Q^2$-behaviour of the form factor. Systematic effects are taken into account by performing a number of fits with cuts for the pion mass and lattice spacing and with different ansätze for the chiral and infinite-volume extrapolations. Our final result for the $z$-expansion coefficients is provided by an Akaike-information-criterion based model average.
