Preliminary calculation of αs from Green functions with dynamical quarks

Abstract

We present preliminary results on the computation of the QCD running cou- pling constant in the ^MOM scheme and Landau gauge with two flavours of dynamical Wilson quarks. Gluon momenta range up to about 7GeV (β = 5.6, 5.8 and 6.0) with a constant dynamical-quark mass. This range already allows to exhibit some evidence for a sizable 1/μ2 correction to the asymptotic behaviour, as in the quenched approximation, although a fit without power corrections is still possible with a reasonable χ2. Following the conclusions of our quenched study, we take into account 1/μ2 correction to the asymptotic behaviour. We find ¤ Nf=2 MS = 264(27)MeV × [a−1(5.6, 0.1560)/2.19GeV], which leads to αs(MZ) = 0.113(3)(4). The latter result has to be taken as a preliminary indication rather than a real prediction in view of the systematic errors still to be controlled. Still, being two sigmas below the experimental result makes it very encouraging.