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Physics Program

A large fraction of the work performed on the Fermilab lattice computers is aimed at the lattice QCD calculations required to extract from experiment the fundamental parameters of the Standard Model, including B and D meson semileptonic and leptonic decay amplitudes, and B-B bar mixing elements.

The most recent work employs a new formulation for unquenched light quarks, improved staggered fermions, which allows lighter quarks and higher precision than obtained in previous calculations. A recent Physical Review Letter, High Precision Lattice QCD Confronts Experiment, showed that the simplest lattice calculations, which agreed only at the 10% level in the quenched approximation, agree to a few per cent in the new calculations. Application of the new methods to a wide variety of applications is in progress.

Recent descriptions of this work have appeared in articles in Nature and in Physics Today.

Single stable-meson masses and decays such as the above are golden quantities for lattice QCD. They are accurately measurable in experiment, with unquenched calculations that are becoming increasingly accurate. Many of the lattice calculations most important to particle physics, such as the calculations required for understanding Bs Bs bar oscillations in the Tevatron, are in this family. As shown in the graph at right (taken from http://arxiv.org/abs/hep-ph/0307195v2) improvements in our understanding of the CKM matrix will increasingly depend on lattice calculations.