OPE, charm-quark mass, and decay constants of D and D_s mesons from QCD sum rules

Understand

We present a sum-rule extraction of the decay constants of the charmed mesons D and D_s from the two-point correlator of pseudoscalar currents.

• First, we compare the perturbative expansion for the correlator and the decay constant performed in terms of the pole and the running MSbar masses of the charm quark.
• The perturbative expansion in terms of the pole mass shows no signs of convergence whereas reorganizing this very expansion in terms of the MSbar mass leads to a distinct hierarchy of the perturbative expansion.
• Furthermore, the decay constants extracted from the pole-mass correlator turn out to be considerably smaller than those obtained by means of the MSbar-mass correlator.