Background.
Although the properties of quarkonia are easy to estimate using potential models,
they are interesting for lattice QCD for just that reason. Before the advent of good
unquenched calculations, potential models enabled one to estimate the effects of the
quenched approximation. Such quantities as αs and the heavy quark masses could
therefore be obtained with reasonable precision before analogous quantities could be
obtained from light quark physics. Unquenched calculations will yield these quan-
tities with accuracies limited only by perturbation theory. In current unquenched
calculations, they serve several additional important purposes. First, because they are
well-understood with potential models, one can expect particular quarkonium proper-
ties to be very sensitive to certain correction operators. For example, the splitting of
the χc states is expected to be very sensitive to the O(v^4) correction ψσ· ∇ × Eψ.
Therefore, quarkonium calculations are important test beds for improved actions.
Second, quarkonium decays test methods analogous to those of phenomenological crucial
heavy-light meson decays: leptonic decays of quarkonia are similar to leptonic decays of
heavy-lights, and electromagnetic transitions of quarkonia are similar to semileptonic
decays of heavy-lights. Thus, a successful quarkonia program bolsters confidence in the
heavy-light program, and hence, lattice CKM determinations. CLEO-c will improve
dramatically the accuracy of these charmonium decays over the next couple of years,
making our calculations of quarkonium properties timely in their own right.
Project Goals.
This project is a companion to the staggered fermion heavy-light meson project of Bailey
et al. All methods, software, and benchmarks are joint between the two proposals, so
the details will not be repeated here. This work and that of the Bailey et al. proposal
use the four component heavy fermions of El-Khadra et al. (the Fermilab fermions) and unquenched improved staggered fermions.
The project will make use of the heavy quark propagators calculated for the Fermilab/MILC heavy-light project.
It will generate the additional heavy propagators that are useful in quarkonium physics.
In particular, it will generate propagators with 2S sources to accompany those generated for the heavy-light project.
2008/2009 Goals.
Abstract of 2008 proposal:
This proposal is part of a coordinated effort to calculate some of the most important
quantities relevant for standard model
phenomenology. We propose a study of the masses of heavy quarkonium
states below open flavor threshold. Quarkonium is ideal for testing
improved heavy quark actions, and verifying that their uncertainties
are well understood. In addition to providing new and precise
determinations of heavy quark masses, comparison with existing and
upcoming experimental results will add an important test of lattice
QCD, aid in the interpretation of problematic excited quarkonium
states, and assist in the discovery of hybrid quarkonium states, both
exotic and nonexotic.
The computational goals of the 2008/2009 proposal were the calculation of the effects of charm/anticharm annihilation on the hyperfine splitting of the 1S state and the study of excited and exotic charmonium states.
2008/2009 Results.
Preliminary results for (1) splittings of the P-wave states and
(2) the effect of the annihilation channel on the hyperfine splitting
were reported at the Lattice 2008 conference. Coding and parameter
tuning for the excited state study is complete
Selected References
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