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Jets at the Tevatron

Jets at the Tevatron. B. Paul Padley Dept of Physics and Astronomy Rice University. Exciting Time. Obviously we have entered an era of new energy and luminosity. Clearly the is a great potential to do new and exciting things And the old stuff even looks new and exciting.

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Jets at the Tevatron

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  1. Jets at the Tevatron B. Paul Padley Dept of Physics and Astronomy Rice University

  2. Exciting Time • Obviously we have entered an era of new energy and luminosity. • Clearly the is a great potential to do new and exciting things • And the old stuff even looks new and exciting. • Probing ~10-19 m scale

  3. Highest mass di-jet event so far Highest mass di-jet event so far (corrected mass = 1364 GeV/c2): r-fview ET = 666 GeV h= 0.43 ET = 633 GeV h= -0.19

  4. D0 Highest Dijet Mass Event 1206 GeV/c2 dijet mass event

  5. Clusters • Use Run II cone algorithm • Combine particles in a R=0.7 cone • Use the four vector of every tower as a seed • Rerun using the midpoints between pairs of jets as seeds • Overlapping jets merged if the overlap area contains more than 50% of lower Pt jet, otherwise particles assigned to nearest jet. Cf. Blazey et al. Hep-ex/0005012v2

  6. Jets Both groups are using E-scheme recombination Cf. Blazey et al. Hep-ex/0005012v2

  7. Inclusive Jet Cross Section Extending Run 1 reach by ~150 GeV Run II Data shown taken between Feb 2002 and summer 2003 (They are planning on new results using Kt algorithm in May)

  8. Inclusive Jet Cross Section • Excitement about Run 1 high ET excess • SM explanation: gluon PDF not well constrained at high x Use EKS pQCD http://zebu.uoregon.edu/~soper/EKSJets/jet.html

  9. Inclusive Jet Cross Section Ratio Both plots the same with extra point on the lower

  10. Inclusive Jet Cross Section Notice forward jets

  11. Inclusive Jet Cross Section

  12. Inclusive Jet Cross Section JES uncertainty <7% dominant contributor to systematic uncertainties

  13. Dijet Cross Section

  14. Dijet Cross Section

  15. Dijet Df Decorrelations Jet 1 In leading order pQCD dijets are back to back Df=p Jet 2

  16. Dijet Df Decorrelations Three jet events in leading order pQCD As Kt goes to 0, Df goes to p If Kt is large Df<<p Jet 1 Jet 3 Df<p Kt Jet 2 Df distribution is directly sensitive to QCD higher order radiation without explicitly measuring the third jet

  17. Dijet Df Decorrelations

  18. Df Decorrelations, Compare to LO

  19. Df Decorrelations, Compare to LO Poor fit to data at low Pt. At higher Pt’s it gets better, especially in the 2.3 to 2.8 regime Same plots as previous page, just spread out for print visibility

  20. Dijet Df Decorrelations

  21. Dijet Df Decorrelations Pythia Tune A reproduces the data best.

  22. Underlying Event Studies Transverse regions are sensitive to underlying event “Back-to-Back” (Df12>150o,ETj2/ETj1>0.8)

  23. Underlying Event Studies Run 2 Min-Bias 0.25 per unit h-f • Direction of leading jet to define 3 fregions

  24. Underlying Event Studies (2) Run 2 data: Current MC with default parameters fail to reproduce data. In Run 1 PYTHIA 6.206 tuned adding multi-parton interactions. • Shows the average charged particle density, dN/dhdf, in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events compared with PYTHIA Tune A and HERWIG after CDFSIM.

  25. Underlying Event Studies (3) PYTHIA tuned (on Run 1 data) reproduces Run 2 data well HERWIG (with no multi-parton interaction) works only at high ETj1. • Average charged PTsum density, dPT/dhdf, in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events compared with PYTHIA Tune A and HERWIG after CDFSIM.

  26. Conclusions • First results have been shown – no surprises • Highest mass DY events have been observed • Jet Energy Scale is dominant error in inclusive cross sections • Pythia Tune A (by Rick Field) on the Run 1 data is reproducing soft data well.

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