$\eta$ and ${\eta }^{\mathrm{\prime }}$ masses and decay constants

We present preliminary results for the masses and decay constants of the $\eta$ and ${\eta }^{\mathrm{\prime }}$ mesons using CLS $N_f=2+1$ ensembles. One of the major challenges in these calculations are the large statistical fluctuations due to disconnected quark loops. We tackle these by employing a combination of noise reduction techniques which are tuned to minimize the statistical error at a fixed cost. On the analysis side we carefully assess excited states contributions by using a direct fit approach.