Lattice QCD studies of Upsilon physics

[摘要] Non-Relativistic QCD (henceforth NRQCD) is a non-relativistic effective theory thatmodels the strong interaction. We use this formulation to perform lattice simulations ofthe bound states of b quarks, known as the Upsilon spectrum. These simulations are performedon a range of gauge ensembles provided by the MILC collaboration that include threeflavours of quark content - one at the approximate mass of the strange quark, and twodegenerate flavours that range from about a half to a tenth of the mass of the strangequark.We implement a random wall algorithm in the creation of our b quark propagators,and develop a technique to combine the random wall with smearing functions, which areused to assist in picking out the relevant quantum numbers in the the resulting mesoncorrelator. This is the first time these techniques have been used in this manner.We employ a Bayesian fitting procedure to extract energies and amplitudes from oursimulated correlators. By using the 2S−1S Upsilon splitting on each configuration, and matchingto experimental results, we are able to extract the lattice spacings for each ensemblefrom which we determine the heavy quark potential scale parameter r1. In concert withresults from our collaborators, we outline the procedure for combining multiple determinationsof r1, and present the collaborative result. We then use this parameter in adetermination of the strong coupling constant αs in the MS scheme.We investigate the dispersion relation of the NRQCD action, and note some undesirablefeatures that we are able to resolve with the precision attainable using the randomwall. We look at a number of ways to address these issues, including non-perturbative andperturbative tuning of coefficients. Using the perturbative coefficients, we then proceedto calculate heavy-heavy currents, which are perturbatively matched to the continuum,and allow us to give results for the Upsilon leptonic width.

[发布机构] University:University of Glasgow;Department:School of Physics and Astronomy

[关键词] physics, lattice, qcd, nrqcd, nonrelativistic, upsilon, quantum chromodynamics, spectroscopy