Non-perturbative renormalization factors of bilinear quark operators for   Kogut-Susskind fermions and light quark masses in quenched QCD
  Light quark masses are computed for Kogut-Susskind fermions by evaluating non-perturbatively the renormalization factor for bilinear quark operators. Calculations are carried out in the quenched approximation at \beta=6.0, 6.2, and 6.4. For the average up and down quark mass we find $m_{\bar MS}(2 GeV)= 4.15(27) MeV$ in the continuum limit, which is significantly larger than $3.51(20) MeV$ ($q^*=1/a$) or $3.40(21) MeV$ ($q^*=\pi/a$) obtained with the one-loop perturbative renormalization factor. 
JLQCD Collaboration: S. Aoki, M. Fukugita, S. Hashimoto, K-I.   Ishikawa, N. Ishizuka, Y. Iwasaki, K. Kanaya, T. Kaneda, S. ...