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Flavor Singlet Meson Mass in the Continuum Limit in Two-Flavor Lattice QCD

We present results for the mass of the eta-prime meson in the continuum limit for two-flavor lattice QCD, calculated on the CP-PACS computer, using a renormalization-group improved gauge action, and Sheikholeslami and Wohlert's fermion action with tadpole-improved csw. Correlation functions are measured at three values of the coupling constant beta corresponding to the lattice spacing a approx. 0.22, 0.16, 0.11 fm and for four values of the quark mass parameter kappa corresponding to mpi over mrho approx. 0.8, 0.75, 0.7 and 0.6. For each beta, kappa pair, 400-800 gauge configurations are used. The two-loop diagrams are evaluated using a noisy source method. We calculate eta-prime propagators using local sources, and find that excited state contributions are much reduced by smearing. A full analysis for the smeared propagators gives metaprime=0.960(87)+0.036-0.248 GeV, in the continuum limit, where the second error represents the systematic uncertainty coming from varying the functional form for chiral and continuum extrapolations.