1. Electron reconstruction efficiency of the ATLAS detector Menno de Bell A CERN summerstudent project under supervision of Pamela Ferrari

2. Introduction Goal Dileptonic ttbar events Tag& probe method Cuts Same sign subtraction Results Conclusion

3. Goal of the project Determining the efficiency of electron reconstruction in the ATLAS detector using ttbar events.

4. Dileptonic ttbar events High abundancy of ttbar events Top decays into bottom + W Bottom creates a jet W either decays hadronically or leptonic

5. Tag & Probe Method Three steps to determine efficiency: 1.Find one well reconstructed lepton: tag it 2.Pick another lepton to probe: probe it to see if it’s good 3.Efficiency given by fraction of good probes Eff = N good /N probed

6. Well reconstructed/good leptons Isolation – Energy deposited in cone Reconstruction Algorithm Transverse energy – Only for tagged leptons

7. Cuts Number of jets (>2) Missing transverse energy Distance to closest jet Invariant mass of three jets Number of b-jets – Depends on b-tagging

8. Same Sign Subtraction Leptons coming from dileptonic events are of opposite sign 50% chance background has same sign Signal estimate by subtracting twice the number of same sign events Eff = N good - 2N good,ss N probed - 2N probed,ss

9. Results: Cutflow NeventsTrig/Jets/EtmProbeOKbtaggingtopmassDrjet 0.05samesign ttbar98995,728771,35434,793802,292271,331436,11830,2 dileptonic1778,681297,74976,94821,83 Zee+jets49439,24257,62140,054,841,130,97 Zmumu+jets48194,841027,17100,42,160,990,50,17 WW331,210,313,560000 Wenu+jets46457626305,732414,8985,4640,7619,110 Wmnu+jets466576,433977,362998,45109,725621,871,69 Wtnu+jets1342003111,42280,754,762,861,43-1,43 Ztt+jets48302,31131,52183,833,651,530,840,48 ZZ116,240,120,080000 ZZ298,82,471,060,030,040,03 ZW11065,383,650,110,080,070,02 ZW262,42,931,970,02 0,01-0,01 sTopS5784976,7780,2363,137,8621,193,16 sTopT303,226,922,11,130,620,34-0,09 hadTop73076,771,7412,226,520,930,520,31

10. Results: Same Sign Subtraction

11. Results: Efficiency

12. Conclusion Efficiency can be calculated with ttbar events – Same sign subtraction works – B-tagging needed