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

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 spring summer2005 version Contents

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

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

Likelihood Function for bbbar ambiguity  is the angle of Wstar Rest Frame

MET Double Gaussian with single mean value (5 parameter)

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

Top Specific Correlation Factor distribution 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 Rec P gen P – Rec P Xaxis value of each bin is weighted mean From takeuchi-san

Mlnb distribution Sim Lev -- top -- other

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

PP W*- t b b W W*+ t b +Z  Wstar Rest Frame W b d u ud Signal Wbb Rest Frame PP W b +Z   b du bb W ud du ud

Signal Wbb  e ttbar Bkgs ?? W+ W-

lepton direction at the Top rest frame PP b l- b l+ +Z t t udud  Top Rest Frame Top quark is polarizing the d-type-quark direction at the top rest frame. -> lepton is boosted d-type-quark direction

W*+ W*- correct wrong cos  lep distribution

Use Kinematics likelihood to the event selection Similar distribution…

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

Mbb distribution We can use this variable for event selection !

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

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

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

} 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

Backup

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

Neutrino solution

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

P ---- W* W* - To have pronounced tendency to separate W*+ and W*- PP W*- t b b l- W*+ t b b l+ +Z correct wrong

P Z *Q ---- correct ---- wrong

W* t b b l M W* 2 > M t 2 +M b 2 ~ M t 2 M W* =q 2 =s ^ W* has the mass as small as possible to keep larger than Mt…?? W* mass

M Using L5 jet No b jet correction

Likelihood … correlation check M W* P Z *Q lep

MET Gaussian Double Gaussian We use this one !

Result of the Likelihood fitting

bbbar ambiguity

Likelihood Function for bbbar ambiguity  is the angle of Wstar Rest Frame

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

M lb distribution W* t b b l Using L5 jet No b jet correction Gen LevSim Lev -- top -- other -- top -- other Use these distribution as the Probability Density Function

cos  b x Q lep PP W*- t b b l- W*+ t b b l+ +Z 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 the Wstar rest frame.  Wstar Rest Frame cos  angle shown in upper figure times lepton charge is the powerful variable to select b-jet which is directory produced form Wstar.

cos  b distribution Gen Lev Sim Lev topother topother ---- W* W* -

cos  b x Q lep distribution Gen Lev -- top -- other Sim Lev -- top -- other Use these distribution as the Probability Density Function

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 !

Top Specific Correction for b-jet

Correlation Factor as the function of Pt Eta

After Correction check

Top Mass Distribution Linear ScaleLog Scale

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

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

64.3% 29.5% 52.4% 19.7% B-tag 45.9% 37.6% SignalW(mu)bb

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

Conclusion  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 2 solution case 0 or 1 solution case

Backup

W* t b b l wrong correct P ---- W* W* - Bug is Fixed !

P Z *Q ---- correct ---- wrong

W* t b b l wrong correct M

Probability Density Function

Neutrino Solution Check Choose Correct Solution Result of the Likelihood fitting What?? P Z =0 ??

-2Log L distribution as the function of P Z First 6 events…

Likelihood distribution for the case of P Z =0 Most likely P Z is really 0 ?? Is this correct??

---- correct ---- wrong corr wrong 72.7% 75.2% Likelihood for Solution corr wrong