Meson Mass Decomposition from Lattice QCD

TL;DR

This paper decomposes meson masses into quark and glue components using lattice QCD, revealing how different contributions vary across meson types and quark masses, including insights into heavy mesons and charmonium.

Contribution

First lattice QCD calculation of meson mass decomposition into quark and glue components, providing detailed insights into their relative contributions.

Findings

Approximately 50% of the pion mass comes from the quark mass term.

For the rho meson, quark energy contributes about half of its mass.

Glue components contribute around 40-50% for both light and heavy mesons.

Abstract

Hadron masses can be decomposed as a sum of quark and glue components which are defined through hadronic matrix elements of QCD operators. The components consist of the quark mass term, the quark energy term, the glue energy term, and the trace anomaly term. We calculate these components for mesons with lattice QCD for the first time. The calculation is carried out with overlap fermion on $2+1$ flavor domain-wall fermion gauge configurations. We confirm that $\sim 50\%$ of the light pion mass comes from the quark mass term and $\sim 10\%$ comes from the quark energy; whereas, while for the $\rho$ meson, the quark energy contributes roughly half of its mass but the quark mass term contributes little. The combined glue components contribute $\sim 40 - 50\%$ for both mesons. It is interesting to observe that the quark mass contribution to the mass of the vector meson is almost linear in quark mass over a large quark mass region below the charm quark mass. For heavy mesons, the quark mass term dominates the masses, while the contribution from the glue components is about $200$ MeV (a bare value around 2GeV) for the heavy pseudoscalar and vector mesons. The charmonium hyperfine splitting is found to be dominated by the quark energy term which is consistent with the picture of the quark potential model.