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 $m_{\bar MS}(2 GeV)= 4.15(27) MeV$inthecontinuumlimit,whichissignificantlylargerthan$3.51(20) MeV$($q^=1/a$)or$3.40(21) MeV$($q^=\pi/a$) obtained with the one-loop perturbative renormalization factor.