Data based nethod for $Z \to \mu^{+}\mu^{-}$ background subtraction in ATLAS detector at LHC

The most copious background in the search of much new physics beyond Standard M odel results from the production of the resonant bb Zo -> mumu final state. In ord er to evaluate and control this background an experimental method is proposed, following a preliminary study. The method takes advantage from the large suppression of the electron decay channel for the signal to be searched, and from the universality of the weak coupling in Z decay. The method is based on the study of a sample of experimental data, for the channel bb Z->ee , not depending on the background channel itself, and in principle avoiding theoretical uncertainties and their propagation to Monte Carlo. The different impact of inner-brem~ (IB) and of detector response on the measured rates of Z decays to electrons and muons is investigated using a full simulation of the ATLAS detector. The extension to other final states as tau tau and heavy flavours, is straightforward.