A study of the eta and eta' mesons with improved staggered fermions
  We report on a high statistics lattice QCD calculation of the mass of the eta and eta' mesons using ASQTAD improved staggered fermions. The calculation used two ensembles with different lattice spacings and pion masses. We also report results for eta-eta' mixing. The results are in satisfactory agreement with other lattice calculations using other fermion formulations and with experiment, given the the unphysical quark masses used. We see no evidence of abnormal behaviour at the lattice spacings studied. 
Eric B. Gregory, Alan C. Irving, Christopher M. Richards and Craig   McNeile
hep-lat