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Study of high pT electrons from Z’ Update

This study provides updates on high pT electrons from Z’ decays, focusing on resolution calculations and reconstruction behavior. It discusses tail distributions, reconstruction improvements, and impacts on energy and pT resolutions. The electron identification efficiency and isolation cuts are also analyzed for better reconstruction efficiency.

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Study of high pT electrons from Z’ Update

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  1. 14 November 2006 Study of high pT electrons from Z’Update Fabienne LEDROIT Julien MOREL CSC note – diphoton dilepton

  2. Data set and Athena version • We use : • Athena version : 11.0.41 • Process : Z’e+e- at 1TeV (Mll > 500 GeV) • Data Set : csc11.005605.Zprime_ee_pythia_chi1000.recon.AOD.v11004205 • Number of events : 24000 Z’ • Cross section = 376.5 fb (mistake done in the last meeting) Signal visible with 1 fb-1

  3. What are the updates ? • In the resolution calculation : • Look at the tails in the DE/E, DpT/pT distribution in the end-cap • Improvement of the fit function • Resolution obtain by fitting with a Gaussian strongly depends on the fit range. • I now use : • whitch take into account the tails in order to extract the Gaussian part of the distribution Gaussian part tails

  4. Long tails in the End-Cap (Electron object matched with the truth) In the last meeting we showed : • DE/E distribution in the different parts of the calorimeter : Overflows Shift • Same behavior forDpT/pT What is this tail in the end-cap ?

  5. Tails come from the crack definition – Energy resolution (Electron matched) If we enlarge the crack (1.4 – 1.61) : Good reconstruction Good reconstruction bad behavior in the crack Poor reconstruction No more tail

  6. Tails come from the crack definition – pT resolution (Electron matched) Same behavior for the pT as for the energy : Good reconstruction Good reconstruction bad behavior in the crack Poor reconstruction No more tail

  7. Impact on the E-resolution versus E (Electrons matched with the truth) • Mean value : • With tracker • 1% Mean value : With tracker  1.1% Values are a slightly different from the last ones because the fit range was not very fine tuned (for the old gaussian fit)

  8. Impact on the pT-resolution versus pT (Electrons matched with the truth) Mean value : Cluster only 1.7% With tracker 0.9% Mean value : Cluster only 1.8% With tracker 1.1% Values are a slightly different from the last ones because the fit range was not very fine tuned (for the old gaussian fit)

  9. Impact on the Z’ invariant mass resolution (Electrons matched with the truth) Id based on tracker • 2 electrons in the barrel : Resolution  (0.8 ± 0.01) % • 1 electron in the barrel and 1 in the end-cap : Resolution  (0.7 ± 0.02) % • 2 electrons in the end-cap : Resolution  (0.8 ± 0.04) % • Good reconstruction except when an electron goes in the crack region (13%)

  10. Electrons identification • In the electron identification : • Last time we used electrons : • Matched with the truth electrons comind from the Z’ ( Dr<0.1 ) • Reconstructed with the egamma algorithm ( author = 1 ) • with IsEm = 0 • Now, we : • Look at the impact of egamma cut on the electron identification efficiency • Look at the impact of matched cut on the electron identification efficiency • Add an isolation cut Id based on tracker

  11. ± g e , Which isolation cut can we use ? With the AOD we have access to EtCone, EtCone20, EtCone40. HCal EtCone = E(cone) – E(box) Cone radius = 0.45 for EtCone 0.2 for EtCone20 0.4 for EtCone40 Box = 57 EM Calo Hadronic leakage Box Cone

  12. Which isolation cut can we use ? Hadronic leakage up to 60 GeV Hadronic leakage up to 20 GeV IsEm 0 IsEm = 0 IsEm = 0 IsEm = 0 Hadronic leakage can be neglected At high ET, EMShower seem to be broader than the Box

  13. Which isolation cut can we use ? We can try with a larger “box” (EtCone40 – EtCone20) : seem to be more clean and efficient. But as it use larger cones, we have to check this efficiency on background.

  14. Impact on the electron selection efficiency We use electrons coming from the Z’ matched with the truth EtCone20/Et < 0.2 EtCone20/Et < 0.2 Average efficiency value around 70% Identification based on the firth sampling and tracker are the main sources of loss

  15. Impact of isolation on the Z’ selection efficiency We use electrons coming from the Z’ matched with the truth Eff EtCone20/Et < 0.2 Mll (GeV) Isolation cut seem to be free but may be very useful to eliminate background

  16. Conclusion and outlook Last meeting results consolidated We have ideas on possible isolation cuts • To do • Study the DY spectrum at mll<500 GeV for 0.1 fb-1 • Look at the trigger efficiencies • Background • K-factors

  17. BACKUP

  18. Which isolation cut can we use ? Hadronic leakage can be neglected At high ET, EMShower seem to be broader than the Box

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