Meson Electromagnetic Form Factors from Lattice QCD

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.

Comments: 6 pages, 5 figures, Proceedings of LATTICE2018