Combination procedure for the precise determination of Z boson parameters from results of the LEP experiments

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.