  We study the moments of hadronic event shapes in $e^+e^-$ annihilation within
the context of next-to-next-to-leading order (NNLO) perturbative QCD
predictions combined with non-perturbative power corrections in the dispersive
model. This model is extended to match upon the NNLO perturbative prediction.
The resulting theoretical expression has been compared to experimental data
from JADE and OPAL, and a new value for $\alpha_s(M_Z)$ has been determined, as
well as of the average coupling $\alpha_0$ in the non-perturbative region below
$\mu_I=2$ GeV within the dispersive model:
\alpha_s(M_Z)&=0.1153\pm0.0017(\mathrm{exp})\pm0.0023(\mathrm{th}),\alpha_0&=0.5132\pm0.0115(\mathrm{exp})\pm0.0381(\mathrm{th}),
The precision of the $\alpha_s(M_Z)$ value has been improved in comparison to
the previously available next-to-leading order analysis. We observe that the
resulting power corrections are considerably larger than those estimated from
hadronization models in multi-purpose event generator programs.

High Energy Physics - Phenomenology