The eta and eta' mesons from lattice QCD

Lattice QCD allows a first-principles study of QCD with the freedom to vary the number and masses of the quarks. I present results on the flavour singlet correlations (this illuminates OZI violating effects) for mesons. Concentrating on the pseudoscalar mesons, the flavour singlet mass splitting ($\eta$, $\eta'$ mass splitting) appears naturally. I also present results on an investigation of decay constants for the $\eta$ and $\eta'$ ($f_{\eta}$) and discuss which quantities may be accessible in future lattice studies. The Witten-Veneziano approach can also be explored by determining the quenched topological susceptibility on a lattice.