Non-perturbative renormalization constants and light quark masses

We present the results of an extensive non-perturbative calculation of the renormalization constants of bilinear quark operators,for the non-perturbatively O(a)-improved Wilson action. The results are obtained at four values of the lattice coupling, by using the RI/MOM and the Ward identities methods. A new non-perturbative,renormalization technique, which is based on the study of the lattice correlation functions at short distance in x-space, is also numerically investigated. We then use our non-perturbative determination of the quark mass renormalization constants to compute the values of the strange and the average up/down quark masses. After performing an extrapolation to the continuum limit, we obtain m<((MS)(s))over bar>ms(2 GeV) = (106 +/- 2 +/- 8) MeV and m<((MS)(l))over bar>(2 GeV) = (4.4 +/- 0.1 +/- 0.4) MeV.