# The pseudoscalar meson electromagnetic form factor at high $Q^2$ from full lattice QCD

## TL;DR

This study uses full lattice QCD to accurately determine the electromagnetic form factor of a light pseudoscalar meson up to high momentum transfer, providing insights into the transition from non-perturbative to perturbative QCD regimes.

## Contribution

First lattice QCD calculation of the pseudoscalar meson form factor up to 6 GeV^2 including sea quarks, controlling discretisation and sea quark effects.

## Key findings

- Q^2F(Q^2) becomes flat between 2 and 6 GeV^2
- Values exceed perturbative QCD expectations at high Q^2
- Results applicable to pion form factor studies

## Abstract

We give an accurate determination of the vector (electromagnetic) form factor, $F(Q^2)$, for a light pseudoscalar meson up to squared momentum transfer $Q^2$ values of 6 $\mathrm{GeV}^2$ for the first time from full lattice QCD, including $u$, $d$, $s$ and $c$ quarks in the sea at multiple values of the lattice spacing. Our results show good control of lattice discretisation and sea quark mass effects. We study a pseudoscalar meson made of valence $s$ quarks but the qualitative picture obtained applies also to the $\pi$ meson, relevant to upcoming experiments at Jefferson Lab. We find that $Q^2F(Q^2)$ becomes flat in the region between $Q^2$ of 2 $\mathrm{GeV}^2$ and 6 $\mathrm{GeV}^2$, with a value well above that of the asymptotic perturbative QCD expectation, but well below that of the vector-meson dominance pole form appropriate to low $Q^2$ values. Our calculations show that we can reach higher $Q^2$ values in future to shed further light on where the perturbative QCD result emerges.