Light quark masses in Nf=2+1 lattice QCD withWilson fermions ALPHA Collaboration

We present a lattice QCD determination of light quark masses with three sea-quark flavours ( Nf = 2 + 1). Bare quark masses are known from PCAC relations in the framework of CLS lattice computations with a nonperturbatively improved Wilson-Clover action and a treelevel Symanzik improved gauge action. They are fully non-perturbatively improved, including the recently computed Symanzik counter-term bA - bP. The mass renormalisation at hadronic scales and the renormalisation group running over a wide range of scales are known nonperturbatively in the Schrodinger functional scheme. In the present paper we perform detailed extrapolations to the physical point, obtaining (for the four-flavour theory) mu/ d(2 GeV) = 3.54(12)(9) MeV and ms(2 GeV) = 95.7(2.5)(2.4) MeV in the MS scheme. For the mass ratio we have ms/mu/ d = 27.0(1.0)(0.4). The RGI values in the three-flavour theory are Mu/ d = 4.70(15)(12) MeV and Ms = 127.0(3.1)(3.2) MeV.