1 / 40

New Kinematics Fitter for Event Selection in Top Quark Analysis

This paper introduces a novel kinematics fitter designed to enhance event selection in top quark analyses, particularly focusing on double-tagged events. It examines modified likelihood distributions, significance estimation, and variations in background rejection using advanced statistical techniques. The study emphasizes improvements in the efficiency of distinguishing signals from backgrounds in complex event scenarios and provides detailed insights into the mass and momentum distributions relevant to the Wbb and ttbar channels.

hewitt
Télécharger la présentation

New Kinematics Fitter for Event Selection in Top Quark Analysis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Single Top Search ~ New Kinematics Fitter for event selection ~ K Nakamura

  2. 61.21 9.5 1.9 0.49 3.3 7.02 ---- 0.6 } 20.67 S/B=7.02/96.6=0.07 S/sq(B)=0.71 S/B=15.3/534.5=0.03 S/sq(B)=0.66 improvement

  3. Mlb distribution Mlnb distribution normalized by # of events of CDFnote At least 1 b-tag

  4. Double tag… At least 1 b-tag S+S S+J double tag

  5. Likelihood for Event Selection 2D Likelihood

  6. distribution MbbGeV MbbGeV PtbbGeV PtbbGeV

  7. -2logL old new simulated simulated simulated

  8. Mlnb distribution Double tag shape

  9. Significance

  10. Mlnb distribution pre tag shape normalized by # of double tag events

  11. Significance

  12. Definition of most significant mass region Width of mass region [GeV] Center of mass region [GeV]

  13. Conclusion No threshold S/sqB=0.75 threshold=1 S/sqB=0.81 TO DO Estimate the significance to fit bkg and signal distribution… Study Event selection to reject ttbar background… Estimate data based background event yield for double tag…

  14. Backup

  15. W boson direction at the W* rest frame Dominant channel of Wbb background is t-channel like upper right feynman diagram. -> W boson direction is close to p or pbar direction

  16. Signal W W f b f b t t d u d P P u W*- W*+ +Z @ Wstar Rest Frame b b Wbb b b b b u d u d f d u d u P P f + - + - +Z W W @ Wbb Rest Frame

  17. cosfw distribution generator level … w/o acceptance cut simulated

  18. cosfw distribution generator level … w/ acceptance cut simulated

  19. cosfwxQlep distribution We can use this variable for event selection !

  20. lepton direction at the Top rest frame @ Top Rest Frame n n l- l+ f d u f u d t t P P b +Z b Top quark is polarizing the d-type-quark direction at the top rest frame. -> lepton is boosted d-type-quark direction

  21. bb system behavior for the event selection -> bb invariant mass in the Wbb background looks much smaller than signal… -> gluon splitting to bbbar is very soft like ISR. -> distance between bb and W of the Wbb bkg is larger than signal

  22. Ptbb Mbb

  23. Collation of Ptbb and Mbb distribution Signal gen Signal simulated Mbb Wbb gen Wbb simulated Ptbb

  24. distance between bb and W

  25. -2logL vs Mlnb signal ttbar wbb wcc **Shape of distribution is made from pretag sample

  26. Significance S/sqB = 0.80

  27. S-channel single top event @ CM Frame n l t W* b b ambiguity CDFNOTE Selection of bjet from top quark t-channel : tagged jet -> 95% s-channel : tagged jet -> 53% top mass resolution +15 GeV Selection of neutrino Pz solution 30% … no solution Mlnb : for 4 cases This Top Mass constraint gave some bias to Mlnb distribution??

  28. Neutrino solution

  29. Likelihood Function for neutrino Pz To define a Likelihood as the function of Neutrino Pz 2 solution case 0 or 1 solution case Move three parameters: METx METy PnZ

  30. bbbar ambiguity

  31. Likelihood Function for bbbar ambiguity f is the angle of b-jet @ Wstar Rest Frame

  32. Top Specific Correction for b-jet

  33. Top Specific Correlation Factor gen P – Rec P Rec P p0=2.12 p1=23.3 p2=0.057 p0=1.83 p1=24.8 p2=0.032 p0=1.31 p1=25.0 p2=0.081 From takeuchi-san From takeuchi-san From takeuchi-san Xaxis value of each bin is weighted mean distribution

  34. Mlnb distribution Sim Lev -- top -- other

  35. B-tag Signal W(mu)bb ttbar 64.3% 52.4% 57.2% 45.9% 37.6% 36.5% 29.5% 19.7% 20.9%

  36. -2Log L distribution as the function of PnZ First 6 events…

  37. Likelihood distribution for the case of PnZ=0 Most likely PnZ is really 0 ?? Is this correct??

  38. Likelihood for Event Selection 2D Likelihood

More Related