Meson Electromagnetic Form Factors from Lattice QCD

TL;DR

This paper uses lattice QCD to calculate meson electromagnetic form factors, providing predictions for experiments and insights into how QCD confinement influences meson structure across various momentum transfer regions.

Contribution

It offers novel lattice QCD calculations of $K^+$, $K^0$, and $ ext{eta}_c$ meson form factors up to high $Q^2$, extending previous work and aiding experimental comparisons.

Findings

$K^+$ form factor predicted for upcoming JLab experiments.

$ ext{eta}_c$ form factor computed up to 25 GeV$^2$, approaching perturbative QCD.

$K^+$ form factor remains larger than asymptotic QCD predictions at high $Q^2$.

Abstract

Lattice QCD can provide a direct determination of meson electromagnetic form factors, making predictions for upcoming experiments at Jefferson Lab. The form factors are a reflection of the bound-state nature of the meson and so these calculations give information about how confinement by QCD affects meson internal structure. The region of high squared (space-like) momentum-transfer, $Q^2$, is of particular interest because perturbative QCD predictions take a simple form in that limit that depends on the meson decay constant. We previously showed in\cite{jonnaff} that, up to $Q^2$ of 6 $\mathrm{GeV}^2$, the form factor for a `pseudo-pion' made of strange quarks was significantly larger than the asymptotic perturbative QCD result and showed no sign of heading towards that value at higher $Q^2$. Here we give predictions for real mesons, the $K^+$ and $K^0$, in anticipation of JLAB results for the $K^+$ in the next few years. We also give results for a heavier meson, the $\eta_c$, up to $Q^2$ of 25 $\mathrm{GeV}^2$ for a comparison to perturbative QCD in a higher $Q^2$ regime.