Abstract
We present a new QCD sum rule with high sensitivity to the continuum regions of charm and bottom quark pair production. Combining this sum rule with existing ones yields very stable results for the MS quark masses, mc(mc) and mb(mb). We introduce a phenomenological parametrization of the continuum interpolating smoothly between the pseudoscalar threshold and asymptotic quark regions. Comparison of our approach with recent BES data allows for a robust theoretical error estimate. The parametric uncertainty due to αs is reduced by performing a simultaneous fit to the most precise sum rules and other high precision observables. This includes a new evaluation of the lifetime of the τ lepton, ττ, serving as a strong constraint on αs. Our results are mc(mc)=1.289+0.040−0.045 GeV, mb(mb)=4.207+0.030−0.031 GeV (with a correlation of 29%), and αs(MZ)[ττ]=0.1221−0.0023+0.0026.
Highlights
We present a new QCD sum rule with high sensitivity to the continuum regions of charm and bottom quark pair production
Αs is quite large at the mass scales of the bottom and charm quarks, questioning the convergence of perturbative QCD (PQCD)
One of these sum rules is new, and its use together with existing ones [6, 7] proves to be a powerful tool to constrain the continuum region of quark pair production. This will be helpful for the case of the b quark for which precise measurements of R(s) or of Rb(s) are unavailable
Summary
We present a new QCD sum rule with high sensitivity to the continuum regions of charm and bottom quark pair production. Αs is quite large at the mass scales of the bottom and charm quarks, questioning the convergence of perturbative QCD (PQCD). This yields αs(MZ ) = 0.1200 ± 0.0028 [3] with very little theoretical uncertainty, but b quark effects are small and mb(MZ ) = 2.67 ± 0.50 GeV [4] is not well constrained.
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