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Data based method for background subtraction: Z → μ + μ -

Data based method for background subtraction: Z → μ + μ -. Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile , Giovanni Nicoletti Laboratori Nazionali di Frascati , Università di Roma La Sapienza, INFN. Outline. Motivation. Example of application: bb Z  m + m -

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Data based method for background subtraction: Z → μ + μ -

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  1. Data based method for background subtraction: Z →μ+μ- Halina Bilokon,Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Laboratori Nazionali di Frascati, Università di Roma La Sapienza, INFN Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  2. Outline • Motivation. • Example of application: bb Z  m+ m- • Method proposed • Software & Generators • Simulation, Reconstruction, Analysis. • Sample • Conclusion and future development Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  3. MonteCarlo Isajet Ariadne Sherpa Cojest • Les Houches Guidebook hep-ph/040345 Jetset Pythia Herwig Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  4. Shower MonteCarlo Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  5. Motivation • It is then extremely important to rely on alternative method to MonteCarlo, as much we can • We propose a method based on a different data sample of experimental data • Only hypothesis: lepton universality. • Example of application: bb Z  m+ m- (most copious background of bb h0/A  m+ m- studies (14/12/2005) S.G. presentation, ATLAS-PHYS-2003-015, June 2003.) Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  6. Signal & background h0 bb→m- m+bb • ~ 0.2 - 0.01 pb (even lower) s ~ 22.8 pb • Zbb →m-m+ bb (Pythia 6.226)AcerMC (v.2.3) interfaced with Pythia 6.2 (hep/ph0405247). Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  7. Background Subtraction Method Precise Knowledge of background is crucial • Experimental method proposed based on Z→ m+m- and Z→ e+ e- • Relying on experimental data • Br( h0→ e+ e-) neglegible • Different Inner Bremsstrahlung Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  8. Z production Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  9. Software Release & Sample • Generation Athena 9.0.4 - Pythia (v.6.226) - Acer (v. 2.3) • Simulation, Digitalization, ReconstructionAthena 10.0.1 • Analysis based on CBNT (root –ntuples). • Final study in scenario ~ 600000 events • In this presentation Lint ~ 20 fb-1 ~ 400000 events Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  10. Study performed • Different Inner Bremsstrahlung Zbb → m-m+ bb (g) Ng ~ 0.086 Nev=464522 Zbb → e-e+ bb (g) Ng ~ 0.157 Nev=442828 • Different Detector Response • The most significative variable of bb h0/A  m+ m- analysis has be chosen Minv as test . • NB. The combination of a same flavor lepton originating from b and one of Z are included inevitably in the plots Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  11. Bremsstrahlung Photons Zbb →m-m+ bb Zbb → e-e+ bb NgMC~ 0.086 NgMC~ 0.157 e Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  12. Bremsstrahlung Photons Zbb →m-m+ bb Zbb → e-e+ bb Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  13. Generator level: Zbb →m-m+ bb Minv(m+m-)g Minv(m+m-) Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  14. Generator level: Zbb →m-m+ bb Minv(m+m-) Minv(m+m-)g Only events with a g of Bremsstrahlung Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  15. Generator level: Zbb → e-e+ bb Minv(e+e-)g Minv(e+e-) Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  16. Generator level: Zbb → e-e+ bb Minv(e+e-)g Minv(e+e-) Only events with a g of Bremsstrahlung Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  17. Generator level: Zbb → e-e+ bb Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  18. Generator level Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  19. Generator level Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  20. Leptons muons electrons Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  21. Photons: Zbb →m-m+ bb Bremsstrahlung photons All photons watch the different scale! Subsample(~25000 ev) PT vs.Distance between g and m Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  22. Photons: Zbb →m-m+ bb All photons Bremsstrahlung photons DR ~ 0.15 Distance between g and m watch the different scale! Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  23. Photons: Zbb → e-e+ bb Bremsstrahlung photons All photons 5x5 cluster in ATLAS watch the different scale! Subsample(~25000 ev) PT vs.Distance between g and e Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  24. Photons: Zbb → e-e+ bb All photons Bremsstrahlung photons DR ~ 0.25 watch the different scale! Distance between g and e Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  25. Photons • If the photon is emitted close to electron, only one cluster is reconstructed and the combined 4-momentum is measured. For the g is effectively absorbed in the same cluster of the electron. • corresponds to a 5x5 cluster in ATLAS. The energy of electron is measured in e.m. calorimeter, q and f are measured in tracker. • Photons, inside cone DR, are taken in account summing their 4-momentum to the 4-momentum of the nearest lepton. • Photons reconstructed are e.m. clusters without track associated (Dh= 0.025,Df =0.05 ) andPT >5GeV, |h| >2.5. Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  26. All Photons: Zbb →m-m+ bb Zbb → e-e+ bb Zbb →m-m+ bb PT g> 5 GeV |h| >2.7 recontructed g Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  27. Reconstruction • Muons: combined reconstruction (inner detector + spectrometer), PT >10 GeV, |h| >2.5. • Electrons: energy measured in calorimeter,(q,f) measured from tracker, PT >10 GeV , |h| >2.5. • Photons: e.m. cluster without track associated : Dh= 0.025, Df =0.05, PT > 5 GeV, |h| >2.5. • Brem photons: >2 leptons reconstructed + • g reconstructed in a cone around lepton direction < DR. • Electrons sample only one cluster is reconstructed. • Muon sample: m track near photon cluster, misidentification. The number events reconstructed with gbrem identified is at percent level. Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  28. Reconstruction: Zbb →m-m+ bb Minv(m+m-) Minv(m+m-)g Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  29. Reconstruction: Zbb →m-m+ bb Minv(m+m-) Minv(m+m-)g Only events with a g of Bremsstrahlung Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  30. Reconstruction: Zbb → e-e+ bb Minv(e+e-)g Minv(e+e-) Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  31. Reconstruction: Zbb → e-e+ bb Minv(e+e-) Minv(e+e-)g Only events with a g of Bremsstrahlung Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  32. Reconstruction Only events with a g of Bremsstrahlung Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  33. Reconstruction The number g bremsstrahlung reconstructed separatly in muons events is higher than electron events, where are mostly absorbed in the electron cluster Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  34. Generation-reconstruction Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  35. Generation-reconstruction Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  36. Conclusions A study for an experimental method of background subtraction is developed based on fully simulated samples, Lint ~ 20 fb-1 of: bb Z  m+ m- and bb Z e+ e- comparing: the Bremsstrahlung of the two samples. the ATLAS detector response. The study is preliminary and needs careful tuning on data collected. DR is an extremely important parameter, that should be carefully tuned. Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  37. Conclusions In the region Minv 98 -135 GeV the ratio is reasonably stable and the effect of Bremsstrahlung is negligible with respect to detector response The same method can be applied to H→ tt and in general to all decays where the electron decay is negligible in the signal. The method relies on lepton universality and needs a good knowledge of detector response for different leptons The method doesn’t need an implementationon MC of higher order corrections Acknowledgements: Borut Kersevan, Dirk Zerwas,Donatella Cavalli Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  38. Riserve • Riserve Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  39. Matching track narrow Dh= 0.025 Df =0.05 • Isolation broad • h= 0.05 Df =0.10 DR =0.07 size of cluster 5x 5 Dh= 0.025 Df =0.05 Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  40. Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

  41. Halina Bilokon, Vitaliano Chiarella, Simonetta Gentile, Giovanni Nicoletti Higgs Meeting 18 April 2006,CERN.

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