Flavour Singlet Mesons in Full QCD on the Lattice
  We apply spectral methods to compute the OZI-rule suppressed loop-loop correlators in the pseudoscalar meson flavour singlet channel. Using SESAM configurations (obtained with two degenerate sea quark flavours on 16x16x16x32 lattices at beta = 5.6 with standard Wilson action), we find for the first time clear evidence for mass plateau formation in the eta' channel of this theory. As a consequence, we observe a clear signal of a mass gap persistent under chiral extrapolation. This sets the stage for a more realistic two-channel approach, where partially quenched strange quarks would be included, in addition to u, d sea quarks. 
K. Schilling, H. Neff, N. Eicker, Th. Lippert (Wuppertal University,   Germany), and J.W. Negele (MIT, Cambridge, Mass.)