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INCLUSIVE-JET AND DIJET CROSS SECTIONS IN DIS AT HERA Paper Presentation

INCLUSIVE-JET AND DIJET CROSS SECTIONS IN DIS AT HERA Paper Presentation. C. Glasman, M. Jimenez, T. Sch örner-Sadenius , J. Terron, T. Theedt ZEUS Monday Meeting DESY, 27. M ärz 2006. OVERVIEW. ¶ Motivation and reminder ¶ Event and jet selection ¶ Data quality

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INCLUSIVE-JET AND DIJET CROSS SECTIONS IN DIS AT HERA Paper Presentation

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  1. INCLUSIVE-JET AND DIJET CROSS SECTIONS IN DIS AT HERAPaper Presentation C. Glasman, M. Jimenez, T. Schörner-Sadenius, J. Terron, T. Theedt ZEUS Monday MeetingDESY, 27. März 2006

  2. OVERVIEW ¶ Motivation and reminder ¶ Event and jet selection ¶ Data quality ¶ Comparisons with second analyses ¶ Data treatment, NLO theory, uncertianties ¶ Applied corrections ¶ Final results ¶ Overview of paper plots ¶ Summary TSS: Inclusive Jets and Dijets in DIS

  3. INTRODUCTION, MOTIVATION ¶ Jets at high values of Q2 in the Breit frame – provide clean tests of pQCD (parton universality, factorisation), – allow access to the strong coupling and to the PDFs. ¶ Especially double-differential cross sections in Q2 and ET (inclusive-jet) or Q2 and  may help to further pin down the PDFs (gluon at high !). ¶ The use of inclusive jets from high-Q2 DIS was very successful in our global QCD fits of the PDFs! ¶ Compared to previous measurements of inclusive and Di-jets at high Q2– we have almost three times the statistics (82pb-2), – we have access to a new kinematic regime (Ep = 820 GeV  920 GeV).– (for dijets) we use a better analysis technique (doing everything in the Breit frame) and constrain the data to a theoretically safer regime (only high Q2, higher transverse energies  reduced uncertainties) TSS: Inclusive Jets and Dijets in DIS

  4. EVENT AND JET SELECTION ¶ Data: ZEUS 98-00, 81.73pb-1, ¶ MC: ARIADNE and LEPTO, each about 5 data luminosity ¶ Trigger: DIS03 (well-reconstructed electron, Q2 > 80 GeV2) ¶ Phase-space selection: – Q2DA > 125 GeV2 (Q2DA < 5000 GeV2 for dijet analysis)– |coshad| < 0.65 ¶ Cleaning cuts: – E’el > 10 GeV, electron isolation– 38 GeV < E-pz < 65 GeV (dijets: 45 GeV < E-pz < 62 GeV) – |Zvtx| < 34 cm – pT/ET < 2.5– rel > 36 cm – yel < 0.95– no second e- candidate ¶ Jet reconstruction: – longitudinally invariant kT cluster algo in Breit frame. – linear jet energy corrections ¶ Jet phase-space: – -2 < Breit < 1.5– ET > 8 GeV (inclusive-jet)– ET,1(2) > 12 (8) GeV (dijet) ¶ Jet Cleaning cuts: – ET,lab > 2.5 (3) GeV–lab < 2.5 (dijet)– events removed if jets too close to electron or lab < -2. Inclusive-jet sample: 19640 events Dijet sample: 3868 events TSS: Inclusive Jets and Dijets in DIS

  5. CONTROL-PLOTS: DIJET, INCL. SAMPLE Inclusive sample well described by both MC models TSS: Inclusive Jets and Dijets in DIS

  6. CONTROL-PLOTS: DIJET SAMPLE 1 Dijet sample well described by both MC models TSS: Inclusive Jets and Dijets in DIS

  7. CONTROL-PLOTS: DIJET SAMPLE (2) Dijet sample well described by both MC models TSS: Inclusive Jets and Dijets in DIS

  8. CONTROL-PLOTS: MIGRATIONS ETC. Migrations well under control; efficiency and purity typically above 40%! TSS: Inclusive Jets and Dijets in DIS

  9. CONTROL-PLOTS: INCLUSIVE-JETS TSS: Inclusive Jets and Dijets in DIS

  10. COMPARISON WITH SECOND ANALYSISfor inclusive-jet analysis Double-diff. inclusive-jet analysis:ET distributions in Q2 bins Good agreement is observed for both analyses. TSS: Inclusive Jets and Dijets in DIS

  11. COMPARISON WITH SECOND ANALYSISdouble-diff. dijet distributions Double-diff. dijet analysis: distributions in Q2 bins Good agreement is observedfor both analyses. TSS: Inclusive Jets and Dijets in DIS

  12. COMPARISON WITH SECOND ANALYSISsingle-differential dijet distributions Good agreement is observed. TSS: Inclusive Jets and Dijets in DIS

  13. DATA TREATMENT, NLO THEORY, UNCERTAINTIES ¶ Data corrections: – for acceptance and efficiency with LEPTO (ARIADNE).– for QED effects. ¶ NLO: DISENT– PDFs: CTEQ6– renormalisation scale: R = sqrt(Q2+ET2) (dijet), = ET (inclusive-jet) also alternatives tested (e.g. R = Q)– factorisation scale: F = Q– corrected for hadronisation effects using ARIADNE ¶ Systematic checks:– EM finder instead of Sinistra  1(3)% – alternative acceptance correction  7(8)%– jet energy scale 1(3)%  5-10%– electron energy scale 1%  1%– variation of selection criteria  2% ¶ Theoretical uncertainties: – scale variation: 0.5,2R 5-10(20)%– PDF uncertainty: 40 sets from CTEQ6  2-4%–S variation with CTEQ6AB  less than 4% TSS: Inclusive Jets and Dijets in DIS

  14. CORRECTIONS 1 inclusive-jet analysis, low Q2 bins All corrections typically below 10%. TSS: Inclusive Jets and Dijets in DIS

  15. CORRECTIONS 2inclusive-jet analysis, high Q2 bins All corrections typically below 10%. TSS: Inclusive Jets and Dijets in DIS

  16. CORRECTIONS 3single-differential dijet analysis acceptance Hadronisation QED Well under control, somewhat larger than for inclusive-jet analysis. TSS: Inclusive Jets and Dijets in DIS

  17. CORRECTIONS 4double-differential dijet analysis acceptance Hadronisation QED Corrections in general well under control. TSS: Inclusive Jets and Dijets in DIS

  18. THEORETICAL UNCERTAINTIES Double-diff. inclusive-jet analysis:ET distributions in Q2 bins– scale uncertainty 8%, decreasing with increasing Q2.– PDF uncertainty 4%, significant at high ET. Double-diff. dijet analysis: distributions in Q2 bins– scale uncertainty 5-20%, large at small .– PDF uncertainty 4%, significant at high . TSS: Inclusive Jets and Dijets in DIS

  19. GLUON-INDUCED EVENT FRACTION Double-diff. inclusive-jet analysis:ET distributions in Q2 bins- gluon fraction decreases with increasing ET and with increasing Q2. Double-diff. dijet analysis: distributions in Q2 bins- gluon fraction decreases with increasing  and Q2. TSS: Inclusive Jets and Dijets in DIS

  20. FINAL RESULTSsingle-differential dijet analysis – 1 TSS: Inclusive Jets and Dijets in DIS

  21. FINAL RESULTSsingle-differential dijet analysis – 2 TSS: Inclusive Jets and Dijets in DIS

  22. FINAL RESULTSsingle-differential dijet analysis – 3 TSS: Inclusive Jets and Dijets in DIS

  23. FINAL RESULTSdouble-differential inclusive-jet analysis TSS: Inclusive Jets and Dijets in DIS

  24. FINAL RESULTSdouble-differential dijet analysis TSS: Inclusive Jets and Dijets in DIS

  25. PLOTS FOR PAPER - 1 TSS: Inclusive Jets and Dijets in DIS

  26. PLOTS FOR PAPER - 2 TSS: Inclusive Jets and Dijets in DIS

  27. PLOTS FOR PAPER - 3 TSS: Inclusive Jets and Dijets in DIS

  28. SUMMARY ¶ Single-differential dijet and double-differential inclusive-jet and dijet cross sections have been measured in high-Q2 DIS in 98-00 data.¶ The data improve previous analyses: - larger statistics (almost factor 3 wrt 96-97 data) - higher center-of-mass energy (920 versus 820 GeV) - improved selection (Breit frame) and tighter cuts (smaller NLO uncertainties) in case of the dijet analysis. ¶ The data are well described by NLO QCD calculations.¶ The double-differential distributions are sensitive to the gluon density in the proton and should thus serve as input to global QCD fits of the PDFs. ¶ The paper and all information presented here (and some more) can be found under: http://www.desy.de/~schorner/dijets/dijets.html TSS: Inclusive Jets and Dijets in DIS

  29. BACKUP TSS: Inclusive Jets and Dijets in DIS

  30. CONTROL-PLOTS: DIJET, INCL. SAMPLE Inclusive sample well described by both MC models TSS: Inclusive Jets and Dijets in DIS

  31. CONTROL-PLOTS: DIJET SAMPLE 1 Dijet sample well described by both MC models TSS: Inclusive Jets and Dijets in DIS

  32. CONTROL-PLOTS: DIJET SAMPLE (2) Dijet sample well described by both MC models TSS: Inclusive Jets and Dijets in DIS

  33. THEORETICAL UNCERTAINTIESfor inclusive-jet analysis TSS: Inclusive Jets and Dijets in DIS

  34. SYSTEMATIC UNCERTAINTIESfor inclusive-jet analysis TSS: Inclusive Jets and Dijets in DIS

  35. SYSTEMATIC UNCERTAINTIESfor inclusive-jet analysis TSS: Inclusive Jets and Dijets in DIS

  36. TRIGGER EFFICIENCYfor dijet analysis Trigger efficiency is 100% for Q2 > 100 GeV2. TSS: Inclusive Jets and Dijets in DIS

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