QCD Analyses and determinations of alpha-s in e+e- Annihilation at energies between 35 and 189 GeV

TL;DR

The paper conducts a comprehensive QCD test using hadronic e+e- data from JADE and OPAL across 35–189 GeV, exploiting jet-multiplicity observables and multiple jet algorithms. It determines alpha_s at each energy via second-order and matched predictions (including NLLA), carefully evaluating hadronization and renormalization-scale uncertainties and combining results through a consistent statistical framework. The global alpha_s(MZ) result, 0.1187^{+0.0034}_{-0.0019}, agrees with the world average and three-loop running, while energy-evolution analyses yield a compatible value around 0.118–0.119, reinforcing QCD’s running coupling. Qualitative MLLA comparisons for mean jet multiplicity provide further insight into non-perturbative effects and local parton-hadron duality. Overall, the work provides a uniform, cross-checked test of QCD over a broad energy range with quantified theoretical and experimental uncertainties.

Abstract

We employ data taken by the JADE and OPAL experiments for an integrated QCD study in hadronic e+e- annihilations at c.m.s. energies ranging from 35 GeV through 189 GeV. The study is based on jet-multiplicity related observables. The observables are obtained to high jet resolution scales with the JADE, Durham, Cambridge and cone jet finders, and compared with the predictions of various QCD and Monte Carlo models. The strong coupling strength, alpha_s, is determined at each energy by fits of O(alpha_s^2) calculations, as well as matched O(alpha_s^2) and NLLA predictions, to the data. Matching schemes are compared, and the dependence of the results on the choice of the renormalization scale is investigated. The combination of the results using matched predictions gives alpha_s(MZ)=0.1187+{0.0034}-{0.0019}. The strong coupling is also obtained, at lower precision, from O(alpha_s^2) fits of the c.m.s. energy evolution of some of the observables. A qualitative comparison is made between the data and a recent MLLA prediction for mean jet multiplicities.

Figures (17)

• Figure 1: The fractions of events with 2, 3, 4, 5 and more than 5 jets as obtained by the JADE jet algorithm are plotted versus $y_{cut}$ at 35, 91 and 189 GeV. Data points are the measurements by the JADE and OPAL experiments. The error bars represent the total errors. Predictions by PYTHIA, HERWIG, ARIADNE and COJETS are shown using lines of different styles.
• Figure 2: In plots (a), (b), (c), (g) and (h), the fractions of events with 2, 3, 4, 5 and more than 5 jets as obtained by the Durham scheme are plotted versus $y_{cut}$ at 35, 91 and 189 GeV. Diagrams (d) through (f) show the distributions in $y_n$ (see Sect. \ref{['ydistlab']}) corresponding to (a), (b) and (c). The presentation is the same as in Fig. \ref{['e0ratefig']}. Small horizontal ticks indicate the size of the statistical errors.
• Figure 3: In plots (a), (b), (c), (g) and (h), jet fractions as obtained by the Cambridge scheme are plotted versus $y_{cut}$ at 35, 91 and 189 GeV as in Fig. \ref{['dratefig']}. Diagrams (d) through (f) show the differential jet fractions $D_n$ (see section \ref{['ydistlab']}) corresponding to (a), (b) and ⁠ (c).
• Figure 4: The fractions of events with 2 or less, 3 and more than 3 jets as obtained by the cone algorithm are plotted in the upper row versus the cone half angle $R$ at 35, 91 and 189 GeV, the jet energy cut-off $\epsilon$ being fixed at 2.5 GeV for $\sqrt{s}$=35 GeV or 7 GeV otherwise. The lower plots show the corresponding fractions versus $\epsilon$ with $R$ kept fixed at 0.7 rad. Data and Monte Carlo predictions are presented in the same form as in figures \ref{['e0ratefig']} through \ref{['cratefig']}.
• Figure 5: The mean jet multiplicities as obtained by the Durham (a) and Cambridge schemes (b) are plotted versus $y_{cut}$ at 35, 91 and 189 GeV. Data and Monte Carlo predictions are presented in the same form as in the previous figures.