An updated analysis using about 1.5 million events recorded at root s = M-Z
with the DELPHI detector in 1994 is presented. Eighteen infrared and colli
near safe event shape observables are measured as a function of the polar a
ngle of the thrust. axis. The data are compared to theoretical calculations
in O(alpha(s)(2)) including the event orientation. A combined fit of alpha
(s) and of the renormalization scale x(mu) in O(alpha(s)(2)) yields an exce
llent description of the high statistics data.
The weighted average from 18 observables including quark mass effects and c
orrelations is alpha(s)(M-Z(2)) = 0.0026. The final result, derived from th
e jet cone energy fraction, the observable with the smallest theoretical an
d experimental uncertainty, is
alpha(s)(M-Z(2)) = 0.1180 +/- 0.0006(exp.) +/- 0.0013(hadr.) +/- 0.0008(sca
le) +/- 0.0007(mass).
Further studies include an alpha(s) determination using theoretical predict
ions in the next-to-leading log approximation (NLLA), matched NLLA and O(al
pha(s)(2)) predictions as well as theoretically motivated optimized scale s
etting methods. The influence of higher order contributions was also invest
igated by using the method of Pade approximants. Average alpha(s) values de
rived from the different approaches are in good agreement.