Flavour Singlet Mesons in full QCD on the Lattice

We apply spectral methods to compute the OZI-rule suppressed loop-loop correlators in the pseudocalar meson flavour singlet channel. Using SESAM configurations (obtained with two degenerate sea quark flavours on 16×32 lattices at β = 5.6, with standard Wilson action), we find for the first time clear evidence for mass plateau formation in the ηchannel 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 the u, d sea quarks.