We study the flavour singlet pseudoscalar mesons from first principles using lattice QCD. With Nf = 2 flavours of light quark, this is the socalled η2 meson and we discuss the phenomenological status of this. Using maximally twisted-mass lattice QCD, we extract the mass of the η2 meson at two values of the lattice spacing for lighter quarks than previously discussed in the literature. We are able to estimate the mass value in the There is considerable interest in understanding hadronic decays involving η and η ′ in the final state. The phenomenological study of hadronic processes involving flavour singlet pseudoscalar mesons makes assumptions about their composition. Here we address the issue of the nature of the η and η ′ from QCD directly, makin
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