Hint of aZ′boson from the CERN LEP II data

Abstract

The many-parametric fits of the LEP2 data on ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$, ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ processes are performed with the goal to estimate the signals of the Abelian ${Z}^{\ensuremath{'}}$ boson. Four independent parameters must be fitted, if the derived already low-energy relations between the ${Z}^{\ensuremath{'}}$ couplings to the standard model fermions are taken into consideration. No signals are found when the complete LEP2 data set for these processes is treated. In the fit of the backward bins, the hint at the $1.3\ensuremath{\sigma}$ confidence level is detected. The ${Z}^{\ensuremath{'}}$ couplings to the vector and axial-vector lepton currents are constrained. The comparisons with the one-parameter fits and with the corresponding LEP1 experiments are fulfilled.