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

2. 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. 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_25TT1.58 JT_45TT26.24 JT_65TT124.67 JT_95TT&JT_125TT241.5  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. 4 Mass cut for each trigger (95% Eff) JT25: 100 Gev (guess) JT45: 160 Gev JT65: 200 Gev JT95: 300 Gev

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

6. 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. 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. 8 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

9. 9 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.

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

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

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

13. 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. 14 Fit to the data B template C template udsg template Data

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

16. 16 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

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

18. 18 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

19. 19 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

20. 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.