-> Experimentalphysik -> Gruppe Drees/Becks -> Wuppertaler DELPHI Gruppe -> Perturbative QCD

A study of the energy evolution of event shape distributions and their means with the DELPHI detector at LEP

R.Reinhardt, U. Flagmeyer, K.Hamacher, O.Passon, and D. Wicke

Infrared and collinear safe event shape distributions and their mean values are determined at centre-of-mass energies between 45 to 202GeV. A phenomenological analysis in view of power correction models including hadron mass effects for both, differential distributions and mean values is presented. Using power corrections alpha_s is extracted from mean values and shapes. As an alternative approach renormalisation group invariance (RGI) is used as an explicit constraint, leading to a consistent description of mean values without need for sizeable power corrections. The QCD beta-function is precisely measured using this approach. From the DELPHI data on 1-Thrust including data of low energy experiments one obtains beta_0 = 7.86 +- 0.32 for the one loop coefficient of the beta-function or, assuming QCD for the number of active flavours n_f = 4.75 +- 0.44 These values agree well with QCD expectation, beta_0=7.67 and n_f=5.

Full Text with Figures

Postscript DELPHI 2001-062 CONF 490 (~1.3MB)

Individual Figures

Figure 1a: Reconstructed centre-of-mass energy
Figure 1b: Simulation of four fermion background and QCD events
Figure 2: energy distribution of selected isolated photon events
Figure 3: Corrections due to mass effects
Figure 4a: Major distributions for 45GeV
Figure 4b: Major distributions for 66GeV
Figure 4c: Major distributions for 76GeV
Figure 4d: Major distributions for 91.2GeV
Figure 5a: Major distributions for 189GeV
Figure 5b: Major distributions for 192GeV
Figure 5c: Major distributions for 200GeV
Figure 5d: Major distributions for 202GeV
Figure 6a: Event shape mean for different observables
Figure 6b: Event shape mean for different observables
Figure 6c: Event shape mean for different observables
Figure 6d: Event shape mean for different observables
Figure 7a: non-perturbative coefficients of the Jet Broadenings
Figure 7b: non-perturbative coefficients of the Jet Broadenings
Figure 8: non-perturbative coefficients of the EEC
Figure 9: shift of the Sudakov shoulder
Figure 10a: mean values of event shapes
Figure 10b: Results of the DW fits
Figure 11a: results for the non-perturbative parameter K_0
Figure 11b: results for alpha_s(M_Z) deduced from Lambda_R
Figure 12a: Comparison of the data on event shape means with the prediction of pure RGI perturbation theory
Figure 12b: Comparison of the data on event shape means with the prediction of pure RGI perturbation theory
Figure 13a: results for C_1/A(full inclusive observables)
Figure 13b: results for C_1/A(different integration intervals of EEC and JCEF)
Figure 14: Results for alpha_s for different observables and methods
Figure 15: results for alpha_0
Figure 16: The running of 1/<1-T> against log(E_cm)

flagmeyer@whep.uni-wuppertal.de

Letzte Änderung: 25 Jun 2001