Pion form factor and charge radius from Lattice QCD at physical point

TL;DR

This paper reports lattice QCD calculations of the pion electromagnetic form factor at the physical point, providing results consistent with experiments and estimating the pion charge radius.

Contribution

First lattice QCD study of pion form factor at the physical point using Wilson-clover and HISQ quarks across multiple lattice spacings.

Findings

Lattice results agree with experimental data.

Estimated pion charge radius is 0.42(2) fm^2.

Studied effects of lattice spacing and quark mass variations.

Abstract

We present our results on the electromagnetic form factor of pion over a wide range of $Q^2$ using lattice QCD simulations with Wilson-clover valence quarks and HISQ sea quarks. We study the form factor at the physical point with a lattice spacing $a=0.076$ fm. To study the lattice spacing and quark mass effects, we also present results for 300 MeV pion at two different lattice spacings $a=0.04$ and 0.06 fm. The lattice calculations at the physical quark mass appear to agree with the experimental results. Through fits to the form factor, we estimate the charge radius of pion for physical pion mass to be $\langle r_{\pi}^2 \rangle=0.42(2)~{\rm fm}^2$.