The electromagnetic form factor of the pion in two-flavour lattice QCD

TL;DR

This paper reports on a lattice QCD calculation of the pion's electromagnetic form factor, achieving high precision near zero momentum transfer and enabling a model-independent determination of the pion charge radius.

Contribution

The study introduces improved techniques using twisted boundary conditions and stochastic sources for accurate form factor calculations at various lattice spacings and pion masses.

Findings

Accurate form factor results near q^2=0

Pion charge radius determined without model dependence

Comparison with NNLO chiral perturbation theory

Abstract

We present the current status of our lattice calculation of the electromagnetic form factor of the pion with two flavours of non-perturbatively O(a)-improved Wilson fermions. Using twisted boundary conditions and stochastic sources we obtain accurate results with a fine momentum resolution near $q^2=0$. This enables the computation of the charge radius without model dependence. The ensembles cover various lattice spacings and pion masses, ranging down to 250 MeV. This allows to compare the data to continuum chiral perturbation theory to NNLO including corrections of finite lattice spacing to perform a simultaneous chiral and continuum extrapolation. An estimate for the systematic error resulting from the extrapolation can be obtained by looking at the spread of results obtained from other functional forms such as polynomials.