# Application of the Covariant Spectator Theory to the study of heavy and heavy-light mesons

## TL;DR

This paper applies the Covariant Spectator Theory to compute heavy and heavy-light meson spectra, achieving accurate results with minimal parameters and highlighting the importance of covariance in predicting spin-dependent interactions.

## Contribution

It introduces a covariant approach to meson spectroscopy that accurately models heavy mesons with few parameters, emphasizing the role of covariance in spin interactions.

## Key findings

- Good fit to meson spectra with three parameters
- Parameters stable across different spectral fits
- Covariance of the kernel predicts spin interactions effectively

## Abstract

As an application of the Covariant Spectator Theory (CST) we calculate the spectrum of heavy-light and heavy-heavy mesons using covariant versions of a linear confining potential, a one- gluon exchange, and a constant interaction. The CST equations possess the correct one-body limit and are therefore well-suited to describe mesons in which one quark is much heavier than the other. We find a good fit to the mass spectrum of heavy-light and heavy-heavy mesons with just three parameters (apart from the quark masses). Remarkably, the fit parameters are nearly unchanged when we fit to experimental pseudoscalar states only or to the whole spectrum. Because pseudoscalar states are insensitive to spin-orbit interactions and do not determine spin-spin interactions separately from central interactions, this result suggests that it is the covariance of the kernel that correctly predicts the spin-dependent quark-antiquark interactions