Next-to-next-leading order correction to 3-jet rate and event-shape distribution

Abstract

The hadronic events from the e + e − annihilation data at the centre-of-mass energies ranging from 60 to 197 GeV were studied. The AMY and OPAL Collaborations offered a unique opportunity to test QCD by measuring the energy dependence of different observables. The coupling constant, α s, was measured by two different methods: first by employing the three-jet observables. Combining all the data, the value of as at next-to-next leading order (NNLO) was determined to be 0.117 ± 0.004(hard) ± 0.006(theo). Secondly, from the event-shape distributions, the strong coupling constant, α s, was extracted at NNLO and it’s evaluation was tested with the energy scale. The results were consistent with the running of α s, expected from QCD predictions. Averaging over different observables, α s was determined to be 0.115 ± 0.007(hard) ± 0.003(theo).