Evidence for eta prime - pion splitting in unquenched lattice QCD

Abstract

We perform an extrapolation from negative to positive flavour numbers of full QCD lattice estimates of the $η'$ mass. The extrapolations are carried out by keeping $ρ$ and $π$ masses at fixed values. We find an $η'$ -- $π$ splitting which shows a flavour dependence consistent with the Witten Veneziano formula based on the $U(1)$ anomaly. The quantitative splitting is consistent with the estimates made in the quenched approximation.