Barate, R (reprint author), IN2P3, CNRS, PHYS PARTICULES LAB, F-74019 ANNECY LE VIEUX, FRANCE.
The total cross section and the forward-backward asymmetry for the process e(+)e --> mu(+)mu(-)(n gamma) are measured in the energy range 20-136 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 luminosity of 143.5 pb(-1). Two different approaches are used: in the first one an exclusive selection of events with hard initial state radiation in the energy range 20-88 GeV is directly compared with the Standard Model predictions showing good agreement. In the second one, all events are used to obtain a precise measurement of the energy dependence of sigma(0) and A(FB)(0) from a model independent fit, enabling constraints to be placed on models with extra Z bosons. (C) 1997 Published by Elsevier Science B.V.