2. Getting sample and code
Download the package
tar xvf tagprobe_istep.tar
.L dataanalyze.C
run()

3. Data Sample
Generated from MC for LHC production with ATLAS detector simulation
******************************************************************************
*Tree :data : data *
*Entries : : Total = bytes File Size = *
* : : Tree compression factor = *
*Br 0 :ele_N : ele_N/I *
*Entries : : Total Size= bytes File Size = *
*Baskets : : Basket Size= bytes Compression= *
* *
*Br 1 :ele_PT : ele_PT[ele_N]/F *
*Entries : : Total Size= bytes File Size = *
*Baskets : : Basket Size= bytes Compression= *
*Br 2 :ele_Eta : ele_Eta[ele_N]/F *
*Entries : : Total Size= bytes File Size = *
*Baskets : : Basket Size= bytes Compression= *
*Br 3 :ele_Phi : ele_Phi[ele_N]/F *
*Entries : : Total Size= bytes File Size = *
*Br 4 :ele_Charge : ele_Charge[ele_N]/I *
*Entries : : Total Size= bytes File Size = *
*Baskets : : Basket Size= bytes Compression= *
*Br 5 :ele_tight : ele_tight[ele_N]/I *
*Entries : : Total Size= bytes File Size = *
*Baskets : : Basket Size= bytes Compression= *
Electron information only:
Momentum
Electric charge
Electron ID_tight
(=1, passing tight selection)

4. Data Composition Mixture of Zee process and QCD dijet process
With some small probability, jet is mis-reconstructed as electron

5. Efficiency Measurement
If directly counting the number of electrons passing the tight selection, we get
Electron sample is not pure, contaminated by jet-faked electron
Too low to be correct!

6. Tag&Probe Applying tag&probe
Some improvement, but still not pure enough

7. Tag&probe with background subtraction
Fit the spectrum to remove the background contribution

8. Question and Task
Any way to reduce the background contribution at selection level?
Narrower window around Z peak?
Charge information?
Is efficiency a constant?
Dependence on the pseudorapidity?
Dependence on the pT?
Uncertainty?
Statistical uncertainty?
Systematic uncertainty?