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تسجيل مستخدم جديدDetermination of the gluon condensate from data in the charm-quark region
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The gluon condensate, $langle frac{alpha_s}{pi} G^2 rangle$, i.e. the leading order power correction in the operator product expansion of current correlators in QCD at short distances, is determined from $e^+ e^-$ annihilation data in the charm-quark region. This determination is based on finite energy QCD sum rules, weighted by a suitable integration kernel to (i) account for potential quark-hadron duality violations, (ii) enhance the contribution of the well known first two narrow resonances, the $J/psi$ and the $psi(2S)$, while quenching substantially the data region beyond, and (iii) reinforce the role of the gluon condensate in the sum rules. By using a kernel exhibiting a singularity at the origin, the gluon condensate enters the Cauchy residue at the pole through the low energy QCD expansion of the vector current correlator. These features allow for a reasonably precise determination of the condensate, i.e. $langle frac{alpha_s}{pi} G^2 rangle =0.037 ,pm, 0.015 ;{mbox{GeV}}^4$.
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