QCD β function with two flavors of dynamical Wilson fermions

We test the asymptotic scaling behavior of state-of-the-art simulations of QCD with two flavors of light Wilson fermions. This is done by matching pi and rho masses on lattices of size 16(3) X 32 and 8(3) x 16. We find that at beta=6/g(2)=5.3 matching is not possible over a range extending down to beta=3.5. The large lattice data at beta=5.5 matches the small lattice values at beta=4.9(1) leading to a shift Delta beta=0.6(1), considerably larger than the perturbative prediction of 0.45. In both cases we conclude that the simulations are very far from the asymptotic scaling region.