Backgrounds

 We measure the fraction and shape of the QCD background in the W sample by using anti-electron cuts, and derive the normalization of the anti-electron sample from the QCD control sample at low Missing Et. Background fraction is

fQCD = (3.64 +- 0.78)%
Fits to the MT, pt(e) and pt(nu) distributions of events passing anti-electron cuts, representing the QCD background in the W sample. The curves give the Monte Carlo parametrization used.

We determine the shape of the QCD background in the dielectron invariant mass by applying antielectron cuts to Z event sample. The fractions are :

fcc-cc = 0.0622 +- 0.0075
fcc-ec = 0.135 +- 0.021
fec-ec = 0.128 +- 0.022
Fits to the dielectron invariant mass distributions of events passing anti-electron cuts, representing the QCD background in the Z sample. The curves give the Monte Carlo parametrization used.

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