Eur. Phys. J. C 22, 331-340 (2001)
DOI: 10.1007/s100520100794
Analytic perturbation theory in analyzing some QCD observables
D.V. ShirkovBogoliubov Laboratory, JINR, 141980 Dubna, Russia
(Received: 30 July 2001 / Published online: 5 November 2001 - © Springer-Verlag / Società Italiana di Fisica 2001)
Abstract
This paper is devoted to the application
of
the recently devised ghost-free analytic perturbation theory (APT)
for the
analysis of some QCD observables. We start with a discussion
of the main
problem of the perturbative QCD, ghost singularities, and with
a resume
of its resolving within the APT.
By a few examples in various energy and momentum transfer
regions
(with the flavor number
f=3,4 and 5) we demonstrate the effect
of the
improved convergence of the APT modified perturbative QCD expansion.
Our first observation is that in the APT analysis the three-loop
contribution (
) is as a rule numerically inessential.
This gives hope for a practical solution of the well-known
problem
of the asymptotic nature of the common QFT perturbation series.
The second result is that the usual perturbative analysis of time-like
events with the large
term
in the
coefficient
is not
adequate at
. In particular, this relates
to
decay.
Then for the "high" (
f=5) region it is shown that the common
two-loop
(NLO, NLLA) perturbation approximation widely used there (at
) for the analysis
of shape/events data contains a systematic negative error at the
1-2 per
cent level for the extracted
values.
Our physical conclusion is that the
value averaged over
the
f=5 data appreciably differs,
,
from the currently accepted "world average"
(=0.118).
© Società Italiana di Fisica, Springer-Verlag 2001
