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Jets and QCD in D0 Experiment

Jets and QCD in D0 Experiment. Physics at Extreme Energies Hanoi, Vietnam July 23, 2000 V. Š im á k Institute of Physics ASCR, Prague for the D Æ Collaborations. Outline. Inclusive Jet Cross Section : at 1800 GeV at 630 GeV Ratio of Inclusive Jet Cross Sections

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Jets and QCD in D0 Experiment

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  1. Jets and QCD inD0 Experiment Physics at Extreme Energies Hanoi, Vietnam July 23, 2000 V. Šimák Institute of Physics ASCR, Prague for the DÆ Collaborations

  2. Outline • Inclusive Jet Cross Section : • at 1800 GeV • at630 GeV • Ratio of Inclusive Jet Cross Sections • Dijet Triple Differential Cross Section • Dijet Mass Spectrum All theoretical comparisons done with JETRAD V. Šimák

  3. y _ p p x z Transverse segmentation Dh x D  = 0.1 x 0.1 h = - ln [ tan (q / 2) ] |h|< 4.2 l int> 7.2 (total) Electrons: sE / E = 15% /ÖE + 0.3% Pions: sE / E = 45% /ÖE + 4%

  4. Inclusive Jet Cross Section at Ös = 1800 GeV ½h½<0.5 ±8% +12% +24% -10% -20% V. Šimák

  5. Inclusive Jet Cross Section at Ös = 1800 GeV (DÆ)½h½<0.5 • JETRAD mF= mR= ETMax /2 , Rsep=1.3, for |h|< 0.5 For all PDF’s probabilities between 47-90% V. Šimák

  6. Inclusive Jet Cross Section at Ös = 630 GeV ½h½<0.5 = 536 nb-1 V. Šimák

  7. Inclusive Jet Cross Section at Ös = 630 GeV • Some discrepancy at low ET, errors are large , but there is overall agreement. V. Šimák

  8. Ratio of Inclusive Jet Cross Sections Same discrepancy exists in ratio of the scaled cross sections. QCD predictions seem to be 20% higher than expected. V. Šimák

  9. Dijet Triple Differential Cross Section 1994-1995 Collider run (run 1b): =92 ± 6 pb-1 preliminary results Require at least two reconstructed jets Trigger Jet: ET > 60 GeV Probe Jet : ET > 30 GeV No restriction on additional jets. Measurement as input to PDF’s: gluon distribution is most interesting. Both experiments use JETRAD for theoretical comparisons with different PDF’s. V. Šimák

  10. OS Dijet Triple Differential Cross Section (DÆ) SS Beam line • Divide data sample into four eta bins: -- 0.0<|h|<0.5, 0.5<|h|<1.0, 1.0<|h|<1.5, 1.5<|h|<2.0 • Divide each eta bin into two subsamples: -- events with 2 jets on the Opposite Side (OS) -- events with 2 jets on the Same Side (SS). • ET of both jets are measured so there are two entries per event into each of the eight the cross sections. • JETRAD using m = E/2 Note that the renormalization and factorization scale are chosen to be: -- mf = mr = E/2 ( max jet ) V. Šimák

  11. Dijet Triple Differential Cross Section (DÆ) 0.0<|h|<0.5 1.0<|h|<1.5 0.5<|h|<1.0 1.5<|h|<2.0 V. Šimák

  12. m= ET/2 Dijet Triple Differential Cross Section (DÆ) 0.0<|h|<0.5 0.5<|h|<1.0 1.0<|h|<1.5 1.5<|h|<2.0 V. Šimák

  13. m= E/2 Dijet Triple Differential Cross Section (DÆ) 0.0<|h|<0.5 0.5<|h|<1.0 1.0<|h|<1.5 1.5<|h|<2.0 V. Šimák

  14. m= E/2 Dijet Triple Differential Cross Section (DÆ) 0.0<|h|<0.5 0.5<|h|<1.0 1.0<|h|<1.5 1.5<|h|<2.0 V. Šimák

  15. Smeared Cross Section Unsmeared Dijet Mass Distribution 200-220 GeV: 8% Error 800-1400 GeV: 30% Error V. Šimák

  16. “Typical DØ Dijet Event” MJJ = 1.18 TeV Q2 = ET,1×ET,2= 2.2x105 GeV2 ET,1 = 475 GeV, h1 = -0.69, x1=0.66 ET,2 = 472 GeV, h2 = 0.69, x2=0.66 V. Šimák

  17. V. Šimák

  18. cos M Compositeness Contact Predictions QCD + V. Šimák

  19. Compositeness CalculationsEichten et al., Rev. Mod. Phys. 56, 579 (84) Eichten et al., Phys. Rev. Lett 50, 811 (83)Chivukula et al., Phys. Lett. B 380, 92 (96)Lee, Phys. Rev. D 55, 2591 (97)Lane, hep-ph/9605257 (96)Suggested Scale: 1.6 TeV (LL)PRL 77, 438(1996)  V. Šimák

  20. Conclusions • 1800 Inclusive Cross Sec. • No significant excess • Excellent agreement with theory • 630 Inclusive Cross Sec. • NLO predictions ~20% high • Experimental measurements consistent • Ratios 630/1800 • NLO predictions ~20% high. • Experimental measurements consistent • Triple Differential Cross Section: • NLO QCD with recent PDF’s (CTEQ3M, CTEQ4M, CTEQ4HJ, MRST,…) with agreement with D0 within the systematic uncertainties • Cross sections for possible inputs to PDF’s • 1800 Dijet Mass • NLO QCD in agreement with the data • Compositeness Scale > 2.4 TeV • no new physics so far

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