Measurement of the Strong Coupling alpha_s from the Four-Jet Rate in e+e- Annihilation using JADE data

TL;DR

This study uses JADE data from $e^+e^-$ annihilation at six energies in the range 14–44 GeV to determine the strong coupling $\alpha_s$ via the four-jet rate $R_4(y_{cut})$ with the Durham algorithm. By combining NLO perturbative QCD with NLLA resummation through a modified R-matching scheme and applying hadronization and detector corrections, the authors extract $\alpha_s$ at each energy and evolve to $M_{Z^0}$, obtaining $\alpha_s(M_{Z^0}) = 0.1159 \pm 0.0004({\rm stat}) \pm 0.0012({\rm exp}) \pm 0.0024({\rm had}) \pm 0.0007({\rm theo})$, in agreement with the world average. The analysis also investigates renormalization-scale choices (optimized and minimal-sensitivity schemes) and confirms that the standard scale variation approach captures the uncertainties. The results demonstrate consistent agreement between data, hadronization models, and QCD predictions at relatively low center-of-mass energies, highlighting the feasibility of precision $\alpha_s$ determinations from jet-rate observables in historic data sets.

Abstract

Data from e+e- annihilation into hadrons collected by the JADE experiment at centre-of-mass energies between 14 GeV and 44 GeV are used to study the four-jet event production rate as a function of the Durham jet algorithm's resolution parameter ycut. The four-jet rate is compared to QCD next-to-leading order calculations including resummation of large logarithms in the next-to-leading logarithmic approximation. The strong coupling measured from the four-jet rate is as(MZ)=0.1159+-0.0004(stat)+-0.0012(expt)+-0.0024(had)+-0.0007(theo) in agreement with the world average.

Figures (6)

• Figure 1: The figures show the four-jet rate distribution corrected for detector effects at hadron-level as a function of the $y_{\mathrm{cut}}$ resolution parameter obtained with the Durham algorithm. The four-jet rate at four average centre-of-mass energies are shown for $\sqrt{s}=14$ to 35 GeV in comparison with predictions based on PYTHIA, HERWIG and ARIADNE Monte Carlo events. The expected $\mathrm{b\bar{b}}$ background is subtracted from the data. The error bars show the statistical (inner part) and the experimental and statistical uncertainties added in quadrature. The panel in each upper right corner shows the differences between data and Monte Carlo, divided by the quadratic sum of the statistical and experimental error. At points with no data events, the difference is set to zero.
• Figure 2: Same as figure \ref{['hadron']} for $\sqrt{s}=38.3$ and 43.8 GeV.
• Figure 3: The plots show the four-jet rate distributions at the hadron-level for $\sqrt{s}=14$ GeV and 22 GeV. The error bars show the statistical (inner part) and the experimental and statistical uncertainties added in quadrature. The solid curve shows the theory prediction after $\chi^{2}$ minimization within the fit range indicated. The dash-dotted lines shows the error band of the four-jet rate prediction with $\alpha_\mathrm{S}(M_{\mathrm{Z^0}})$ being the current world average value and its error bethke04.
• Figure 4: Same as figure \ref{['fit_plot']} for $\sqrt{s}=34.6$, 35, 38.3 and 43.8 GeV.
• Figure 5: The values for $\alpha_\mathrm{S}$ at the various energy points. The errors show the statistical (inner part) and the total error. The full and dash-dotted lines indicate the current world average value of $\alpha_\mathrm{S}(M_{\mathrm{Z^0}})$bethke04 with error. The results at $\sqrt{s}=34.6$ and 35 GeV have been combined for clarity. The results from the LEP experiments ALEPH aleph249, DELPHI delphir4 and OPAL OPALPN527 are shown as well.