A Study of Event Shapes and Determinations of alpha_s using data of e^+e^- Annihilations at sqrt{s} = 22 to 44 GeV

TL;DR

This study uses JADE e+e- data at 22–44 GeV to extract αs through event-shape observables measured with +NLLA QCD calculations, correcting distributions for detector effects and hadronisation. The analysis yields αs(22 GeV) = 0.161^{+0.016}_{-0.011}, αs(35 GeV) = 0.143^{+0.011}_{-0.007}, and αs(44 GeV) = 0.137^{+0.010}_{-0.007}, in agreement with historical PETRA results and the QCD running when compared with LEP data. In addition, mean values of observables are confronted with analytic QCD predictions including power corrections for hadronisation. The work demonstrates consistent, lower-uncertainty determinations of αs over a broad energy range and reinforces the validity of the QCD energy dependence across 22–44 GeV.

Abstract

Data recorded by the JADE experiment at the PETRA e^+e^- collider were used to measure the event shape observables thrust, heavy jet mass, wide and total jet broadening and the differential 2-jet rate in the Durham scheme. For the latter three observables, no experimental results have previously been presented at these energies. The distributions were compared with resummed QCD calulations (O(alpha_s^2)+NLLA), and the strong coupling constant alpha_s(Q) was determined at different energy scales Q=sqrt{s}. The results, α_s(22 GeV) = 0.161 ^{+0.016}_{-0.011}, α_s(35 GeV) = 0.143 ^{+0.011}_{-0.007}, α_s(44 GeV) = 0.137 ^{+0.010}_{-0.007}, are in agreement with previous combined results of PETRA albeit with smaller uncertainties. Together with corresponding data from LEP, the energy dependence of alpha_s is significantly tested and is found to be in good agreement with the QCD expectation. Similarly, mean values of the observables were compared to analytic QCD predictions where hadronisation effects are absorbed in calculable power corrections.