The total cross section and the forward-backward asymmetry for the process
are measured in the energy range 60-140 GeV by reconstructing the effective centre-of-mass energy
after initial state radiation. The analysis is based on the data recorded with the ALEPH detector at LEP between 1990 and 1995, corresponding to a total integrated
... [Show full abstract] luminosity of 143.5 . The full statistical power of the event sample has been used and a precise measurement of the energy dependence of and is obtained from a model independent fit, enabling constraints to be placed on models with extra Z bosons.