1. The Matrix Method Data-driven method of estimating the W→lv and QCD multijet contributions to sample S’.

2. 2 Lepton selection efficiency in W + jets Use Monte Carlo to obtain ε W : l W represents the number of leptons in the Monte Carlo W+jets sample which pass the loose lepton cuts l W ’ represents the number of leptons in the W+jets sample which also pass the tight lepton cuts ε W = l W’ / l W

3. 3 Lepton selection efficiency in QCD multijets Use data sample with MET < 10 GeV to obtain ε QCD : l QCD represents the number of leptons in the QCD sample which pass the loose lepton cuts. l QCD ’ represents the number of leptons in the QCD sample which pass the tight lepton cuts ε QCD = l QCD ’ / l QCD

4. 4 Data samples S contains N events which passed the preselection cuts with the loose lepton cuts. N = N QCD + N W S’ contains N’ events which passed the preselection cuts with tight lepton cuts. N’ = N QCD ’ + N W ’ N’= ε QCD N QCD + ε W N W

5. 5 Number of signal and background events The number of W→lv events in the data sample S’ is then: N W ’ = ε W N W N W ’= ε W (ε QCD N – N’) / (ε QCD – ε W ) The number of QCD multijets in S’ is: N QCD ’ = ε QCD N QCD N QCD ’ = ε QCD (N’ – ε W N) / (ε QCD – ε W )