Paper detail

Charm and Bottom Masses from Sum Rules with a Convergence Test

In this talk we discuss results of a new extraction of the MS-bar charm quark mass using relativistic QCD sum rules at O(as**3) based on moments of the vector and the pseudoscalar current correlators and using the available experimental measurements from e+e- collisions and lattice results, respectively. The analysis of the perturbative uncertainties is based on different implementations of the perturbative series and on independent variations of the renormalization scales for the mass and the strong coupling following a work we carried out earlier. Accounting for the perturbative series that result from this double scale variation is crucial since some of the series can exhibit extraordinarily small scale dependence, if the two scales are set equal. The new aspect of the work reported here adresses the problem that double scale variation might also lead to an overestimate of the perturbative uncertainties. We supplement the analysis by a convergence test that allows to quantify the overall convergence of QCD perturbation theory for each moment and to discard series that are artificially spoiled by specific choices of the renormalization scales. We also apply the new method to an extraction of the MS-bar bottom quark mass using experimental moments that account for a modeling uncertainty associated to the continuum region where no experimental data is available. We obtain m_c(m_c) = 1.287 +- 0.020 GeV and m_b(m_b) = 4.167 +- 0.023 GeV.