Combination procedure for the precise determination of Z boson parameters from results of the LEP experiments
ALEPH Collaboration, DELPHI Collaboration, L3 Collaboration, OPAL Collaboration, the LEP Electroweak Working Group
TL;DR
The paper addresses the problem of obtaining the most precise Z-boson parameters by combining LEP I measurements from four experiments while properly accounting for correlated systematics. It develops a model-independent fit framework that maps realistic observables to pseudo-observables such as $m_Z$, $Γ_Z$, $σ_h^0$, $R_ℓ^0$, and $A_{FB}^{0,ℓ}$ and performs a global combination across experiments with a rigorous treatment of radiative corrections via electroweak form factors. Key contributions include the detailed methodology for the combination, additional fitting results, and cross-checks within the Minimal Standard Model framework. The work enhances electroweak precision tests by providing robust, high-accuracy determinations of Z-boson parameters and a template for combining complex collider data with correlated uncertainties.
Abstract
The precise determination of the Z boson parameters from the measurements at the Z resonance by the four collaborations ALEPH, DELPHI, L3 and OPAL in e+e- collisions at the large electron positron collider LEP at CERN is a landmark for precision tests of the electroweak theory. The four experiments measured quantities which were used to extract the mass and width of the Z boson, the hadronic cross-section at the pole of the resonance, the ratio of hadronic and leptonic decay widths, and the leptonic forward-backward asymmetries at the pole. The combination procedure based on these parameters is presented in this paper.