Unquenched Charmonium with NRQCD - Lattice 2000

TL;DR

This paper reports on lattice NRQCD simulations of charmonium, analyzing quenched and unquenched effects, and quantifies systematic uncertainties affecting hyperfine splittings.

Contribution

It provides the first detailed comparison of quenched and unquenched NRQCD results for charmonium spectra, highlighting quenching effects and systematic uncertainties.

Findings

Quenching causes about 10% change in hyperfine splittings.

Improving the NRQCD evolution equation affects hyperfine splittings by up to 20 MeV.

Estimated radiative corrections could be as large as 40%.

Abstract

We present results from a series of NRQCD simulations of the charmonium system, both in the quenched approximation and with n_f = 2 dynamical quarks. The spectra show evidence for quenching effects of ~10% in the S- and P-hyperfine splittings. We compare this with other systematic effects. Improving the NRQCD evolution equation altered the S-hyperfine by as much as 20 MeV, and we estimate radiative corrections may be as large as 40%.