Properties of the $\eta$ and ${\eta }^{\prime }$ mesons: Masses, decay constants and gluonic matrix elements

Abstract

We present results for the $\eta$ and ${\eta }^{\prime }$ masses and their four independent decay constants at the physical point as well as their anomalous gluonic matrix elements $a_{{\eta }^{(\prime )}}$. The chiral and continuum limit extrapolation is performed on twenty-one $N_f=2+1$ Coordinated Lattice Simulations (CLS) ensembles with non-perturbatively improved Wilson fermions at four different lattice spacings and along two trajectories in the quark mass plane, including one ensemble very close to physical quark masses. For the first time the decay constants are determined directly from the axialvector matrix elements without model assumptions. This allows us to study their QCD scale dependence and to determine all low-energy constants contributing at next-to-leading order in large-$N_c$ ChPT at a well defined QCD renormalization scale. We also discuss higher excited states in the $1400\mathrm{MeV}$ region.

Comments: 16 pages, 9 figures. Joint proceedings for talks at the 38th International Symposium on Lattice Field Theory, LATTICE2021, 26th-30th July, 2021, Zoom/Gather@Massachusetts Institute of Technology