A non-perturbative determination of bg

Close to the continuum limit, lattice QCD with mass-degenerate Wilson quarks can be described by Symanzik's effective continuum action, which contains the dimension 5 operator, tr( ).Its effect can be eliminated by an O( q ) rescaling of the bare lattice coupling constant.Until recently, the corresponding improvement coefficient, g , was only known perturbatively to 1-loop order and an estimate of the remaining uncertainty is the dominant systematic error in the ALPHA collaboration's recent determination of ( ) with the decoupling method [1].To remove this error we have determined g non-perturbatively for the corresponding parameter range.We here briefly review improvement conditions for g , perform a perturbative test and report on our non-perturbative results for g .