Light quark masses in N_f=2+1 lattice QCD with Wilson fermions

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