/ Experiment-HEP hep-ex/0002026

Consistent measurements of alpha(s) from precise oriented event shape distributions

Abreu, P. ; Adam, W. ; Adye, T. ; Adzic, P. ; Albrecht, Z. ; Alderweireld, T. ; Alekseev, G.D. ; Alemany, R. ; Allmendinger, T. ; Allport, P.P. ; Almehed, S. ; Amaldi, U. ; Amapane, N. ; Amato, S. ; Anassontzis, E.G. ; Andersson, P. ; Andreazza, A. ; Andringa, S. ; Antilogus, P. ; Apel, W.D. ; Arnoud, Y. ; Asman, B. ; Augustin, J.E. ; Augustinus, A. ; Baillon, P.

Published in: Eur.Phys.J.
Year: 2000
Vol.: C14
Page No: 557-584
Pages: 51

Abstract: An updated analysis using about 1.5 million events recorded at $\sqrt{s} = M_Z$ with the DELPHI detector in 1994 is presented. Eighteen infrared and collinear safe event shape observables are measured as a function of the polar angle of the thrust axis. The data are compared to theoretical calculations in ${\cal O} (\alpha_s^2)$ including the event orientation. A combined fit of $\alpha_s$ and of the renormalization scale $x_{\mu}$ in $\cal O(\alpha_s^2$) yields an excellent description of the high statistics data. The weighted average from 18 observables including quark mass effects and correlations is $\alpha_s(M_Z^2) = 0.1174 \pm 0.0026$. The final result, derived from the jet cone energy fraction, the observable with the smallest theoretical and experimental uncertainty, is $\alpha_s(M_Z^2) = 0.1180 \pm 0.0006 (exp.) \pm 0.0013 (hadr.) \pm 0.0008 (scale) \pm 0.0007 (mass)$. Further studies include an $\alpha_s$ determination using theoretical predictions in the next-to-leading log approximation (NLLA), matched NLLA and $\cal O(\alpha_s^2$) predictions as well as theoretically motivated optimized scale setting methods. The influence of higher order contributions was also investigated by using the method of Pad\'{e} approximants. Average $\alpha_s$ values derived from the different approaches are in good agreement.

Note: Revised

Total numbers of views: 2244
Numbers of unique views: 851
e-proceeding