Unquenched Charmonium with NRQCD

TL;DR

This study uses improved lattice NRQCD to analyze charmonium spectra, revealing quenching effects and other systematic uncertainties, emphasizing the need for comprehensive approaches in heavy-quark simulations.

Contribution

The paper provides detailed lattice NRQCD results for charmonium, including dynamical quarks and systematic effect estimates, advancing understanding of quenching and other uncertainties.

Findings

Quenching effects cause about 10% variation in hyperfine splittings.

Choice of tadpole factor influences spin splittings by 10-20%.

Radiative corrections could impact results by up to 40%.

Abstract

We present the results from a series of lattice simulations of the charmonium system using a highly-improved NRQCD action, both in the quenched approximation, and with n_f = 2 light dynamical quarks. The spectra show some evidence for quenching effects of roughly 10% in the S- and P-hyperfine spin splittings---probably too small to account for the severe underestimates in these quantities seen in previous quenched charmonium simulations. We also find estimates for the magnitude of other systematic effects---in particular, the choice of the tadpole factor can alter spin splittings at the 10-20% level, and radiative corrections may be as large as 40% for charmonium. We conclude that quenching is just one of a collection of important effects that require attention in precision heavy-quark simulations.