Lattice QCD calculation of the pion charge radius using a model-independent method

TL;DR

This paper introduces a model-independent lattice QCD method to calculate the pion charge radius with reduced statistical errors, avoiding complex momentum extrapolations and derivative computations, and validates it against traditional approaches.

Contribution

The paper presents a new, simpler lattice QCD method for calculating the pion charge radius that improves statistical precision without additional propagator inversions or derivatives.

Findings

Results are consistent with traditional methods.

Statistical errors are reduced by 1.5-1.9 times.

Errors range from 2.1% to 4.6% across ensembles.

Abstract

We use a method to calculate the hadron's charge radius without model-dependent momentum extrapolations. The method does not require the additional quark propagator inversions on the twisted boundary conditions or the computation of the momentum derivatives of quark propagators and thus is easy to implement. We apply this method to the calculation of pion charge radius $\langle r_\pi^2\rangle$. For comparison, we also determine $\langle r_\pi^2\rangle$ with the traditional approach of computing the slope of the form factors. The new method produces results consistent with those from the traditional method and with statistical errors 1.5-1.9 times smaller. For the four gauge ensembles at the physical pion masses, the statistical errors of $\langle r_\pi^2\rangle$ range from 2.1% to 4.6% by using $\lesssim50$ configurations. For the ensemble at $m_\pi\approx 340$ MeV, the statistical uncertainty is even reduced to a sub-percent level.