2vtx tagged dibjets mass cross section measurement univeristy of notre dame
DESCRIPTION
2vtx tagged diBjets mass cross section measurement Univeristy of Notre Dame Hong Luo Mar 3 th 2005. OUTLINE Data selection. Mass Trigger Turn on Curve and Mass cut. Unsmeared 2vtx tagged dijet mass cross section. MC Study: 2vtx Tag variable: 2D decay length Significance . - PowerPoint PPT PresentationTRANSCRIPT
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2vtx tagged diBjets mass cross section measurement
Univeristy of Notre Dame
Hong Luo Mar 3th 2005
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OUTLINE
Data selection.
Mass Trigger Turn on Curve and Mass cut.
Unsmeared 2vtx tagged dijet mass cross section.
MC Study:
2vtx Tag variable: 2D decay length Significance.
MC prediciton of Tagging rates. ( Eff & Purity ).
MC driven B,C & udsg Jet/Event Templates.
Fitting to the data:
Chisq Fitting .
Likelihood Fitting .
Mass resolution and Energy Smearing. (not finished yet)
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Data Sample Selection All QCD trigger data (by d0correct v-00-00-06) up to April, 2004 in Common Sample Group: ~32Million events .
Total Luminosity: pb^(-1)
JT_25TT 1.58
JT_45TT 26.24
JT_65TT 124.67
JT_95TT&JT_125TT 241.5
Secondary Vertices skimmed:
Removed bad events. (offline data quality: SMT,CAL,CFT,MUO &JET)
one of the 2 leading jets contained a secondary vertex.
Central region requirement: Both jets with |Rapidity|<0.8
Final Data: 472 K events
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Mass cut for each trigger (95% Eff)
JT25: 100 Gev (guess)
JT45: 160 Gev
JT65: 200 Gev
JT95: 300 Gev
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•241.5 pb^(-1).
•Statistical errors only.
•No energy smearing correction
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P14.07.00 MC SamplePythia bb inclusive:
80Gev < Pt < 160Gev
160Gev < Pt <320Gev
320Gev < Pt <980Gev
Pythia cc inclusive:
80Gev < Pt < 160Gev
160Gev < Pt <320Gev
320Gev < Pt <980Gev
Pythia qcd inclusive:
40Gev < Pt < 80Gev, 80Gev < Pt < 160Gev
160Gev < Pt <320Gev
320Gev < Pt <980Gev
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Jet Type:
b quark parent Jet ( no restriction on radiation )
c quark parent Jet ( no restriction on radiation )
udsg Jet ( udsg parent w/o heavy radiation )
b radiation Jet ( udsg parent with b radiation )
c radiation Jet ( udsg parent with c radiation )
udsg Jet: b radiation Jet: c radiation Jet = 171816:2923:5909
Event Type:
B event ( both jets are b quark parent jets )
C event ( both jets are c quark parent jets)
udsg event ( both jets are udsg jets )
B radiation event ( both jets are b radiation jets ) ignorable
C radiation event ( both jets are c radiation jets ) ignorable
udsg event: B radiation event: C radiation event = 72872: 59:148
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2vtx tag variable:
ln(2D decay length significance)
Different shape between b,c&udsg jets.
Independent of Jet Pt.
Ln(2dsig)
MC driven Jet Templates
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MC driven Event Template: ln(2dlSig) Jet0 vs Jet1
B event
udsg event
C event
Variable: Ln(2dlSig).
2 dimension: X: Jet0 vs Y Jet1.
Bad statistics.
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B Event
Double 2vtx tagged
No cut on 2dlSig
B Event
Double 2vtx tagged
Ln(2dlSig)>3.4
B Eff
B Eff B Purity
B Purity
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C Event
Double 2vtx tagged
No cut on 2dLSig
C Event
Double 2vtx Tagged
Ln(2dlsig)>3.4
C Eff
C Eff
C Purity
C Purity
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udsg Purity
udsg Purity
udsg Event
Double 2vtx tagged
No cut on 2dLSig
udsg Event
Double 2vtx Tagged
Ln(2dlsig)>32
udsg Eff
udsg Eff
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•MC prediction of double 2vtx tagged B Eff and Purity as a function of ln(2dlSig) of both Jets.
•It shows that the B purity will be above 68% in all mass region without losing much efficiency by cut of 3.4.
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Fit to the data
B template C template
udsg template Data
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Chisqrt Fitting
Y Projection
100 bins
Y Projection
50 bins
Total chisq = 3787.12
Total chisq = 1262.12
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Refined the C Event templates
MC C event tmplate--- event based
++ jet based
--- event based
++ jet based
Refined/Simulated C event tmplate
X projection
Y projection
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MC B event tmplate--- event based
++ jet based
--- event based
++ jet based
X projection
Y projection Refined/Simulated B event tmplate
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Refined the udsg Event templates
MC udsg event tmplate--- event based
++ jet based
--- event based
++ jet based
X projection
Y projection
Refined/Simulated udsg event tmplate
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Likelihood Fitting Result
likelihood fit is much stable than chisq fit when dealing with the low statistics 2 dimensional fitting.
100 bins
50 bins
2.0<ln(2dlsig)<4.0
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Summary and Follow up
The MC study and Data fitting showed that by applying double 2vtx tag and making suitable tag variable cut, we can get a high B purity diBjet sample while still keeping a reasonable efficiency. The compromise between purity and efficiency need to be determined.
MC driven templates need to be cross checked with data driven one if statistics allows.
Begined to do mass resolution study. Will apply energy smearing correction once the study is finished.
Will get a final diBjet Mass cross section plots after that. And compare it to the theoretical curve.