S fromSpectroscopy with dynamical Wilson Fermions

We estimate the QCD coupling constant from a lattice calculation of the bottomonium spectrum. The second order perturbative expansion of the pla- quette expectation value is employed to determineS at a scale set by the 2S-1S and 1P-1S level splittings. The latter are computed in NRQCD in a dynamical gauge field background with two degenerate flavours of Wilson quarks at intermediate masses and extrapolated to the chiral limit. Com- bining the Nf = 2 result with the quenched result at equal lattice spacing we extrapolate to the physical number of light flavours to find a value of � (5) (mZ) = 0.1118(17). The error quoted covers both statistical and system- atic uncertainties in the scale determination. An additional 5% uncertainty