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Lattice QCD studies of Upsilon physics

Kendall, Iain D. (2010) Lattice QCD studies of Upsilon physics. PhD thesis, University of Glasgow.

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Abstract

Non-Relativistic QCD (henceforth NRQCD) is a non-relativistic effective theory that models the strong interaction. We use this formulation to perform lattice simulations of the bound states of b quarks, known as the Upsilon spectrum. These simulations are performed on a range of gauge ensembles provided by the MILC collaboration that include three flavours of quark content - one at the approximate mass of the strange quark, and two degenerate flavours that range from about a half to a tenth of the mass of the strange quark. 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 are used to assist in picking out the relevant quantum numbers in the the resulting meson correlator. 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 our simulated correlators. By using the 2S−1S Upsilon splitting on each configuration, and matching to experimental results, we are able to extract the lattice spacings for each ensemble from which we determine the heavy quark potential scale parameter r1. In concert with results from our collaborators, we outline the procedure for combining multiple determinations of r1, and present the collaborative result. We then use this parameter in a determination of the strong coupling constant αs in the MS scheme. We investigate the dispersion relation of the NRQCD action, and note some undesirable features that we are able to resolve with the precision attainable using the random wall. We look at a number of ways to address these issues, including non-perturbative and perturbative tuning of coefficients. Using the perturbative coefficients, we then proceed to calculate heavy-heavy currents, which are perturbatively matched to the continuum, and allow us to give results for the Upsilon leptonic width.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: physics, lattice, qcd, nrqcd, nonrelativistic, upsilon, quantum chromodynamics, spectroscopy
Subjects: Q Science > QC Physics
Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
Supervisor's Name: Davies, Professor Christine
Date of Award: 2010
Depositing User: Mr Iain D Kendall
Unique ID: glathesis:2010-2280
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2010
Last Modified: 10 Dec 2012 13:53
URI: http://theses.gla.ac.uk/id/eprint/2280

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