Determination of gammaZ interference in e+e annihilation at LEP.pdf

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN-EP/2000-084 June 29, 2000 Determination of γ /Z interference + − in e e annihilation at LEP 0 0 0 2 l u J 3 L3 Collaboration 1 v 6 0 0 7 0 0 0 / Abstract x e - p An S–Matrix ansatz is used to determine the mass and width of the Z boson, e as well as the contributions of γ /Z interference and Z boson exchange to fermion– h : pair production. For this purpose we use hadron and lepton–pair production cross v i sections and lepton forward–backward asymmetries that have been measured with X the L3 detector at centre–of–mass energies between 87 GeV and 189 GeV. r a Submitted to Phys. Lett. B Introduction The successful operation of LEP has allowed a precise measurement of fermion–pair production, + − ¯ e e → ff, at centre–of–mass energies near the Z resonance. The mass and the total and partial widths of the Z boson have been determined with excellent accuracy. The Standard Model [1, 2] is confirmed with high precision by the experimental results of L3 [3] and other experiments [4–7]. In these analyses, the contribution of the interference between the photon and the Z boson exchange amplitudes is fixed to the Standard Model expectation. In this paper, we use an S–Matrix [8] approach to determine the contributions of γ /Z in- terference and Z boson exchange, thus reducing the number of theoretical assumptions. At centre–of–mass energies well above the