The Light Quark Masses from Lattice Gauge Theory

We study the masses of the light quarks with lattice QCD. Most of the dependence on the lattice spacing a, observed previously with Wilson fermions, is removed by an $O(a)$ corrected action. In the quenched approximation, we obtain a strange quark MS̄ mass m̄ₛ(2GeV)0ex0ex=0ex0ex95(16) MeV, and an average of the up and down quark masses m̄ₗ(2GeV)0ex0ex=0ex0ex3.6(6) MeV. Correcting for quenching, the masses likely are 20% to 40% smaller: 54<m̄ₛ(2GeV)<92 MeV and 2.1<m̄ₗ(2GeV)<3.5 MeV. We argue that most lattice determinations are consistent with these low values, which are outside the range conventionally given.