Search for a Z' at the Z resonance

Abstract

The search for an additional heavy gauge boson Z′ is described. The models considered are based on either a superstring-motivated E₆ or on a left-right symmetry and assume a minimal Higgs sector. Cross sections and asymmetries measured with the L3 detector in the vicinity of the Z resonance during the 1990 and 1991 running periods are used to determine limits on the Z-Z′ gauge boson mixing angle and on the Z′ mass. For Z′ masses above the direct limits, we obtain the following allowed ranges of the mixing angle, θ_M at the 95% confidence level: -0.004 ≤ θ_M ≤ 0.015 for the x model, -0.003 ≤ θ_M ≤ 0.020 for the φ model, -0.029 ≤ θ_M ≤ 0.010 for the η model, -0.002 ≤ θ_M ≤ 0.020 for the LR model.