Abstract
We present results for the η′ meson and the topological susceptibility in Nf = 2 flavour lattice QCD. The results are obtained using Wilson twisted mass fermions at maximal twist with pion masses ranging from 340 MeV down to the physical point. A comparison to literature values is performed giving a handle on discretisation effects.
Highlights
Due to the persisting 3 − 5 σ deviation in the anomalous magnetic moment of the muon aμ between theory and experiment there is considerable interest in the decays η → γ γ and η → γ γ
We have found in Refs. [2, 10] that this approach works very well for the η2 meson in N f = 2 flavour QCD as well as for η and η mesons in N f = 2 + 1 + 1 flavour QCD
In addition we show results for Wilson twisted mass fermions with N f = 2 dynamical quark flavours without clover term taken from Ref. [10]
Summary
Due to the persisting 3 − 5 σ deviation in the anomalous magnetic moment of the muon aμ between theory and experiment there is considerable interest in the decays η → γ γ and η → γ γ. [2] the corresponding mixing has been studied for three values of the lattice spacing and a large, but still unphysical range of pion mass values in N f = 2 + 1 + 1 flavour QCD. The η2 and the η meson have in common that both receive significant fermionic disconnected contributions to their correlation functions Their masses are expected to differ only by 200 MeV, since the strange quark is expected to contribute significantly less than the light quarks [9]. Since the η2 meson is tightly connected to topology, we augment this study by measuring the topological susceptibility as well For this purpose we apply gradient flow techniques [12] and compare to results available in the literature
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