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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.