Single Top Search

1. Single Top Search ~ New Kinematics Fitter and ttbar bkg~ K Nakamura

2. Contents Pointed out previous meeting… • MET fit function • Top specific correction factor • W boson direction at the W* rest frame • lepton direction at the Top rest frame • Use Kinematics likelihood to the event selection • Mbb distribution for the event selection ttbar background ttopvl: Mtop=175 GeV Generated by Pythia MC version 5.3.3 spring summer2005 version

3. 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??

4. 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

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

6. MET Double Gaussian with single mean value (5 parameter)

7. Top Specific Correlation Rec P gen P rec bPt [GeV] gen bPt [GeV]

8. 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

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

10. 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

11. Signal W W f b b f 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

12. Signal Bkgs ttbar W+ W- Wbb e m ??

13. lepton direction at the Top rest frame @ Top Rest Frame n n l- f l+ f d u 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

14. cos flep distribution W*+ correct W*- wrong

15. Use Kinematics likelihood to the event selection Similar distribution…

16. Mbb distribution for the event selection -> bb invariant mass in the Wbb background looks much smaller than signal…

17. Mbb distribution We can use this variable for event selection !

18. ttbar background Mlnb distribution normalized by # of events of CDFnote At least 1 b-tag

19. 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%

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

21. 61.21 8.4 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

22. Backup

23. 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??

24. Neutrino solution

25. 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

26. PnZ @GenLev To have pronounced tendency to separate W*+ and W*- n n l- l+ t t W*- W*+ b b b b wrong correct ---- W*+ ---- W*- P P +Z

27. PnZ *Qlep @Sim ---- correct ---- wrong

28. W* mass n l t W* b MW*2> Mt2+Mb2~ Mt2 b ^ MW* =q2=s W* has the mass as small as possible to keep larger than Mt…??

29. MW* @Sim Using L5 jet No b jet correction

30. Likelihood … correlation check MW* PnZ *Qlep

31. MET Gaussian We use this one ! Double Gaussian

32. Result of the Likelihood fitting

33. bbbar ambiguity

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

35. Using L5 jet n l t W* b b B-jet Pt distribution No b jet correction Gen Lev Sim Lev -- top -- other -- top -- other Use these distribution as the Probability Density Function

36. Using L5 jet n l t W* b b Mlb distribution No b jet correction Gen Lev Sim Lev -- top -- other -- top -- other Use these distribution as the Probability Density Function

37. cosfb x Qlep @ Wstar Rest Frame n n l- l+ t t W*- W*+ f b b P P f +Z b b tb production process has the V-A coupling, so it is easy for the b-jet to be produced in the direction of quark in proton, and bbar-jet to be produced in the direction of anti-quark in anti-proton @ the Wstar rest frame. cosfangle shown in upper figure times lepton charge is the powerful variable to select b-jet which is directory produced form Wstar.

38. cosfb distribution top other Gen Lev ----W*+ ---- W*- top other Sim Lev

39. cosfb x Qlep distribution Sim Lev Gen Lev -- top -- other -- top -- other Use these distribution as the Probability Density Function

40. Parameter correlation These figure shows some correlations between the Likelihood parameters…… But Likelihood is only used as the choosing bbbar ambiguity, so we use this likelihood !

41. Top Specific Correction for b-jet

42. Correlation Factor as the function of Pt Eta

43. After Correction check

44. Top Mass Distribution Linear Scale Log Scale

45. Wbb background Shape Use MC Wbb+0j bkg ----Wbb ---- Signal Normalization is not correct…

46. Mlnb distribution normalized by # of events of CDFnote At least 1 b-tag Wbb 198.5 events s-channel 15.00 events ----Wbb ---- Signal

47. Signal W(mu)bb B-tag 64.3% 52.4% 45.9% 37.6% 29.5% 19.7%

48. Double tag… At least 1 b-tag S+S S+J double tag ----Wbb ---- Signal ----Wbb ---- Signal Enhancement !?

49. Conclusion 2 solution case 0 or 1 solution case • We developed new likelihood fitter without using top mass constraint Make Likelihood fitter like blow : For the 75.2% events of the 2 solution events we can choose the correct solution. • After decided neutrino Pz, we can choose the correct b-jet from the top quark for the 81% of the total events. • But Mlnub distribution is not so improved… • We will try to check correlation between the likelihood variables and top mass

50. Backup