Pion structure from improved lattice QCD: form factor and charge radius at low masses

The charge form factor of the pion is calculated in lattice QCD. The non-perturbatively improved Sheikholeslami-Wohlert action is used together with the $\mathcal{O}(a)$ improved vector current. Other choices for the current are examined. The form factor is extracted for pion masses from 970 MeV down to 360 MeV and for momentum transfers $Q^2 \leq 2 \mathrm{GeV}^2$. The mean square charge radius is extracted, compared to previous determinations and its extrapolation to lower masses discussed.