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2vtx tagged diBjets mass cross section measurement Univeristy of Notre Dame

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 .

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2vtx tagged diBjets mass cross section measurement Univeristy of Notre Dame

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  1. 2vtx tagged diBjets mass cross section measurement Univeristy of Notre Dame Hong Luo Mar 3th 2005

  2. 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)

  3. 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

  4. Mass cut for each trigger (95% Eff) JT25: 100 Gev (guess) JT45: 160 Gev JT65: 200 Gev JT95: 300 Gev

  5. 241.5 pb^(-1). • Statistical errors only. • No energy smearing correction

  6. P14.07.00 MC Sample • Pythia 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

  7. 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

  8. MC driven Jet Templates Ln(2dsig) • 2vtx tag variable: • ln(2D decay length significance) • Different shape between b,c&udsg jets. • Independent of Jet Pt.

  9. MC driven Event Template: ln(2dlSig) Jet0 vs Jet1 C event B event udsg event • Variable: Ln(2dlSig). • 2 dimension: X: Jet0 vs Y Jet1. • Bad statistics.

  10. B Event Double 2vtx tagged No cut on 2dlSig B Purity B Eff B Event Double 2vtx tagged Ln(2dlSig)>3.4 B Eff B Purity

  11. C Event Double 2vtx tagged No cut on 2dLSig C Eff C Purity C Event Double 2vtx Tagged Ln(2dlsig)>3.4 C Eff C Purity

  12. udsg Event Double 2vtx tagged No cut on 2dLSig udsg Purity udsg Eff udsg Event Double 2vtx Tagged Ln(2dlsig)>32 udsg Purity udsg Eff

  13. 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.

  14. Fit to the data B template C template Data udsg template

  15. Chisqrt Fitting Total chisq = 3787.12 Y Projection 100 bins Total chisq = 1262.12 Y Projection 50 bins

  16. Refined the C Event templates MC C event tmplate --- event based ++ jet based X projection Refined/Simulated C event tmplate --- event based ++ jet based Y projection

  17. MC B event tmplate X projection --- event based ++ jet based Y projection Refined/Simulated B event tmplate --- event based ++ jet based

  18. Refined the udsg Event templates --- event based ++ jet based MC udsg event tmplate X projection --- event based ++ jet based Refined/Simulated udsg event tmplate Y projection

  19. Likelihood Fitting Result 100 bins 2.0<ln(2dlsig)<4.0 likelihood fit is much stable than chisq fit when dealing with the low statistics 2 dimensional fitting. 50 bins

  20. 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.

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