Adjoint sources, disconnected loops and other fruit of lattice QCD

We undertake a comprehensive study of the gluelump mass spectrum, exploring the spin structure of the state. We use five lattice spacings from which we extract continuum values for the state splittings, with high statistics employed at β = 6.0. We conduct a low statistics study of a related and previously unexamined lattice state, which we term the adjoint meson. We find that this state is fractionally more massive than the gluelump on the lattices considered, with indications that the splitting is greater than the pion mass at β = 6.0. We investigate a sum rule approach to determining hadronic mass dependencies on the masses of the constituent quarks. We apply this formalism to the b meson spectrum, examining the derivative taken with respect to the valence quark mass in quenched lattice QCD. Subsequently we turn our attention to the pion, and its dependence on the quark mass parameter used in full QCD simulations. Here we employ a Z2 noise method to calculate the propagators needed to construct the relevant correlation functions. Though our determination here is different from that of finite difference methods and our calculation is one of low statistics, there is some discrepancy with the finite difference approach. We see evidence that the correlators employed yield different measurements on quenched and dynamical gauge configurations which are otherwise similar in their observables. We employ the same Z2 method to conduct a preliminary study of the η' meson mass in full QCD. We introduce related source pairs to minimise the variance of the disconnected loop operators that are employed. We are able to obtain estimates of the mass from a very modest number of gauge configurations and purely local operators. We did not observe any evidence of unquenching from the measurements obtained, though statistical noise dominated the signal in the region where definitive effects would be seen. (author)