Strange quark condensate from QCD sum rules to five loops

It is argued that it is valid to use QCD sum rules to determine the scalar and pseudoscalar two-point functions at zero momentum, which in turn determine the ratio of the strange to non-strange quark condensates R-su = <(s) over bars >/<(q) over barq > with (q = u, d). This is done in the framework of a new set of QCD Finite Energy Sum Rules (FESR) that involve as integration kernel a second degree polynomial, tuned to reduce considerably the systematic uncertainties in the hadronic spectral functions. As a result, the parameters limiting the precision of this determination are Lambda(QCD), and to a major extent the strange quark mass. From the positivity of R-su there follows an upper bound on the latter: (m(s)) over bar( 2 GeV) <= 121 ( 105) MeV, for Lambda(QCD) = 330 (420) MeV.