Light Meson Form Factors at near Physical Masses

TL;DR

This study uses lattice QCD to calculate the electromagnetic form factors of the rho meson and pion at near-physical masses, providing precise theoretical data that aligns with recent experimental measurements of the rho meson’s magnetic dipole moment.

Contribution

It presents the first lattice QCD calculation of rho meson and pion form factors at near-physical quark masses, with improved control over excited state contamination and reduced uncertainties.

Findings

Calculated rho meson g-factor g_rho = 2.21(8)

Results agree with experimental measurements

Achieved access to low Q^2 values at near-physical masses

Abstract

The ability for most hadrons to decay via strong interactions prevents the direct measurement of their electromagnetic properties. However, a detailed understanding of how these resonant states feature in scattering processes can allow one to disentangle such information from photo production processes. In particular, there has been increasing interest in the determination of magnetic dipole moments using such methods. In a recent study, Gudino et al. provide the first experimental determination of the magnetic dipole moment of the rho meson. To facilitate a comparison with this experimental determination, we present a calculation of the rho meson and pion electromagnetic form factors calculated in the framework of Lattice QCD. Using the PACS-CS 2+1 flavour full QCD gauge field configurations, we are able to access low $Q^2$ values at near-physical quark masses. Through the use of variational techniques, we control excited state systematics in the matrix elements of the lowest-lying states and gain access to the matrix elements of the first excited state. Our determination of the rho meson $g$-factor $g_{\rho} = 2.21(8)$ is in excellent agreement with this experimental determination, but with a significantly smaller uncertainty.