CERN Accelerating science

Article
Report number	CERN-OPEN-98-001 ; WU-B-97-38
Title	New Results on $\alpha_{s}$ from DELPHI
Author(s)	Hahn, S (Wuppertal U.)
Publication	1999
Imprint	1 Dec 1997
Number of pages	5
In:	International Europhysics Conference on High-Energy Physics, Jerusalem, Israel, 19 - 25 Aug 1997, pp.509-512
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LEP ; DELPHI
Abstract	Recent studies of the strong coupling \as using the DELPHI detector at LEP \cite{pap1,pap2} are reviewed. For the analysis of the data at $ \sqrt{s} = M_Z $ recorded in 1994, a large number of shape observables and their dependence on the event orientation are measured and compared to theoretical calculations in $ { \cal O } ( \alpha_s^2 ) $ . The adjustment of the renormalization scale $ \mu $ turns out to be of major importance. Only a poor description of the data can be achieved if the so-called physical scale $ \mu^2 = Q^2 $ is applied, whereas a combined fit of $ \alpha_s $ and the renormalization scale value yields an excellent description of the high statistics data. For these scale values perfect consistency of the fit values of $ \alpha_s(M_Z) $ is obtained for all event shape observables considered. The running of $ \alpha_s $ is measured from the DELPHI data at $ \sqrt{s} $ = 130 GeV - 172 GeV. Here an analytical power ansatz for the hadronization corrections is compared with hadronization corrections obtained by using Monte Carlo generators.