Flavor singlet pseudoscalar masses in N-f=2 QCD - art. no. 074503

We perform a lattice mass analysis in the flavor singlet pseudoscalar chann el on the SESAM and T chiL full QCD vacuum configurations, with 2 active fl avors of dynamical Wilson fermions at beta =5.6. At our inverse lattice spa cing, a(-1)approximate to2.3 GeV, we retrieve by a chiral extrapolation to the physical light quark masses the value m(eta') = 3.7(-4)(+8)m(pi). A cru de extrapolation from (N-f = 3) phenomenology would suggest m(eta') approxi mate to 5.1m(pi) for N-f = 2 QCD. are verify that the mass gap between the singlet state eta' and the pi flavor triplet state is due to gauge configur ations with nontrivial topology.