Measurement of alpha_s(M_Z^2) from Hadronic Event Observables at the Z^0 Resonance

TL;DR

This study measures the strong coupling constant at the Z-boson mass using hadronic decays recorded by the SLD detector. It analyzes a broad set of observables—event shapes, jet rates, particle correlations, and angular energy flow—and compares data to perturbative QCD predictions at fixed order and with resummation, including multiple matching schemes. Carefully correcting for detector effects and hadronization, the authors find consistent $alpha_s(M_Z^2)$ values across observables, though theory uncertainties from uncalculated higher orders dominate. The final result, $alpha_s(M_Z^2) = 0.1200 \pm 0.0025 (exp) \pm 0.0078 (theor)$, emphasizes the impact of higher-order corrections and the value of combining fixed-order and resummed QCD for precision tests of the Standard Model.

Abstract

The strong coupling alpha_s(M_Z^2) has been measured using hadronic decays of Z^0 bosons collected by the SLD experiment at SLAC. The data were compared with QCD predictions both at fixed order, O(alpha_s^2), and including resummed analytic formulae based on the next-to-leading logarithm approximation. In this comprehensive analysis we studied event shapes, jet rates, particle correlations, and angular energy flow, and checked the consistency between alpha_s(M_Z^2) values extracted from these different measures. Combining all results we obtain alpha_s(M_Z^2) = 0.1200 \pm 0.0025(exp.) \pm 0.0078(theor.), where the dominant uncertainty is from uncalculated higher order contributions.