We explore the effect of higher order operators in the non-relativistic formulation of QCD (NRQCD). We calculated masses in the b \bar b spectrum using quenched gauge configurations at beta = 6.0 and two different NRQCD actions which have been corrected to order mv^4 and mv^6. The two-point functions are calculated in a gauge invariant fashion. We find the general structure of the spectrum to be the same in the two cases. Using the P - 3S1 splitting we determine the inverse lattice spacings to be 2.44(4) GeV and 2.44(5) GeV for the mv^4 and mv^6 actions, respectively. We do observe shifts in the spin splittings. The hyperfine splitting is reduced by approximately 4 MeV, while the fine splitting is down by up to 10 MeV, albeit with large statistical errors.
@article{arxiv.hep-lat/9706003,
title = {Upsilon Spectrum from NRQCD with Improved Action},
author = {UKQCD Collaboration and T. Manke and I. T. Drummond and R. R. Horgan and H. P. Shanahan},
journal= {arXiv preprint arXiv:hep-lat/9706003},
year = {2015}
}
Comments
11 pages, LaTeX2e , 4 figures, uses styles [11pt, a4wide, epsf]. A minor typo in figure 2 has been corrected