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Tevatron in Run 2

Tevatron in Run 2. Major upgrades of the Tevatron for Run II will result in a large increase in the expected delivered luminosity for both CDF and D0 Run 1 110 pb -1 ( lum > 10 31 cm -2 s -1 ) Run IIa: 2 fb -1 Run IIb: 15 fb -1 an increase in the center-of-mass energy from 1.8 to 1.96 TeV

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Tevatron in Run 2

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  1. Tevatron in Run 2 • Major upgrades of the Tevatron for Run II will result in • a large increase in the expected delivered luminosity for both CDF and D0 • Run 1 110 pb-1 ( lum > 1031cm-2s-1) • Run IIa: 2 fb-1 • Run IIb: 15 fb-1 • an increase in the center-of-mass energy from 1.8 to 1.96 TeV • big deal for high ET jets • Main injector leads to increase in luminosity • of factor of 5 (initial goal is 1032 cm-2 s-1) • Recycler leads to additional factor of 2 • (re-cool antiprotons from Tevatron) • Initially 36X36 bunches at 396 ns spacing • Ultimately 141X121 at 132 ns

  2. Run 2 Luminosity Goals

  3. CDF in Run 2 • Detector underwent a major upgrade between Run 1 and Run 2 (~$120M) • Brand new systems include: • Silicon • Central Open-cell Tracker • End-plug and mini-plug calorimeters (coverage up to h of 5.5) • Time-of-flight • Forward muon • Luminosity monitor • DAQ, trigger etc • Detector commissioning is complete • Now taking physics quality data

  4. Installation of silicon into CDF

  5. Rolling in for collisions

  6. QCD in Run 1 • The Tevatron Collider serves as arena for precision tests of QCD with photons, W/Z’s, jets • Highest Q2 scales currently achievable (searches for new physics at small distance scales) • Sensitivity to parton distributions over wide kinematic range • 2 scale problems: test effects of soft gluon resummation • Diffractive production of W/Z, jets, heavy flavor • Dynamics of any new physics will be from QCD; backgrounds to any new physics will be from QCD processes • Data compared to NLO, resummed, leading log Monte Carlo, fixed order calculations

  7. QCD at the Tevatron Overall, the data from CDF and D0 agree well with NLO QCD Some puzzles resolved: • W + jet(s): R10 Some puzzles remain: • Jet excess at high ET/mass?? • Gluon distribution at large x? • 630 GeV jet cross section and xT scaling • Comparison of kT inclusive jet cross section and NLO theory • Heavy flavor cross sections Some theory work needs to be done: • Inclusive photon cross section Some searches still continue: • BFKL effects

  8. Example:Jets at the Tevatron • Both experiments compare to NLO QCD calculations • D0: JETRAD, modified Snowmass clustering(Rsep=1.3, mF=mR=ETmax/2 • CDF: EKS, Snowmass clustering (Rsep=1.3 (2.0 in some previous comparisons), mF=mR=ETjet/2 • In Run 1a, CDF observed an excess in the • jet cross section at high ET, outside the • range of the theoretical uncertainties shown

  9. Similar excess observed in Run 1B

  10. Exotic explanations

  11. Non-exotic explanations Modify the gluon distribution at high x

  12. Tevatron Jets and the high x gluon • Best fit to CDF and D0 central jet cross sections provided by CTEQ5HJ pdf’s • …but this is not the central fit; extra weight given to high ET data points; need a more powerful sample

  13. DØ Preliminary Run 1B • 0.0    0.5 • 0.5    1.0 • 1.0    1.5 • 1.5    2.0 • 2.0    3.0 d2 dET d (fb/GeV) Nominal cross sections & statistical errors only ET (GeV) D0 jet cross section as function of rapidity JETRAD m=ETmax/2 CTEQ4HJ provides best description of data

  14. Chisquares for recent pdf’s • For 90 data points, are the chisquares • for CTEQ4M and MRSTgU “good”? • Compared to CTEQ4HJ?

  15. D0 jet cross section • CTEQ4 and CTEQ5 had CDF and D0 central jet cross sections in fit • Statistical power not great enough to strongly influence high x gluon • CTEQ4HJ/5HJ required a special emphasis to be given to high ET data points • Central fit for CTEQ6 is naturally HJ-like • c2 for CDF+D0 jet data is 113 for 123 data points

  16. So is this the end of the story? • You need to be careful that you are not mistaking old physics for new physics • …but you also have to be careful that you are not labelling potential new physics as old physics • Consider the remaining uncertainty on the parton distribution functions

  17. PDF Uncertainties • Use Hessian technique (T=10) with the CTEQ6 pdf formalism

  18. Gluon Uncertainty • Gluon is fairly well-constrained up to an x-value of 0.3 • New gluon is stiffer than CTEQ5M • not quite as stiff as CTEQ5HJ • But a great deal of uncertainty remains for the high x gluon, and thus for the predictions for the high ET jet cross section

  19. Luminosity function uncertainties at the Tevatron

  20. Luminosity Function Uncertainties at the LHC

  21. MRST2001/CTEQ6M comparison for D0 jets

  22. MRST2001J • Fit to the jet data gives a c2 of 118 (for 113 points) compared to 170 • as = .121 • But gluon has a kink at low Q, leading to a shoulder at higher Q • Fit rejected • But an artifact of too strict a parametrization? • We get a kink in CTEQ6 gluon if we use MRST parametrization

  23. MRST2001J: Comparison to CDF/D0 jets

  24. MRST2001J/CTEQ6M Comparisons

  25. Compare CTEQ6 to MRST • Main difference is the gluon at high x

  26. Jets at 630 GeV • Jet measurements at 630 GeV don’t agree well with NLO QCD predictions

  27. xT scaling D0 sees a similar disagreement (but different behavior at low ET?) • xT scaling ratio of 1800 to 630 GeV jet cross sections also doesn’t agree with NLO QCD

  28. Underlying Event Studies in CDF • Jet events at the Tevatron consist of: • 2->2 hard scatter • initial and final state radiation • semi-hard scatters (multiple parton scattering) • beam-beam remnant interactions Underlying event energy (multiple parton scattering, beam-beam remnants, and (part of) initial and final state radiation) must be subtracted from jet energies for comparison of jet cross sections to NLO QCD predictions (largest uncertainty for low ET) Interesting interface between perturbative and non-perturbative physics

  29. Underlying Event Studies in CDF • 2 complementary studies • first examines jet event structure from 1 GeV to 50 GeV looking at towards, away and transverse regions in phi for central rapidities • second examines jet events over the range from 50 GeV to ~300 GeV looking in 2 cones at same h as lead jet and at +/- 90 degrees in phi away, again in the central region • Both analyses use charged track information (SpTtracks) and compare their results to predictions from leading log Monte Carlos

  30. Charged particle multiplicity

  31. PYTHIA: Multiple Parton Interactions and new HERWIG! Pythia uses multiple parton interactions to enhace the underlying event. Herwig MPI J. M. Butterworth J. R. Forshaw M. H. Seymour Multiple parton interaction more likely in a hard (central) collision! Hard Core

  32. PYTHIA 6.206 Defaults • Plot shows “Transverse” <Nchg> versus PT(chgjet#1) compared to the QCD hard scattering predictions of PYTHIA 6.206 (PT(hard) > 0) using the default parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L. PYTHIA default parameters Constant Probability Scattering Default parameters give very poor description of the “underlying event”! Note Change PARP(67) = 4.0 (< 6.138) PARP(67) = 1.0 (> 6.138)

  33. Tuned PYTHIA 6.206 • Plot shows “Transverse” <Nchg> versus PT(chgjet#1) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA 6.206 (PT(hard) > 0, CTEQ5L). PYTHIA 6.206 CTEQ5L Old PYTHIA default (less initial-state radiation) New PYTHIA default (less initial-state radiation)

  34. Tuned PYTHIA 6.206 vs HERWIG 6.4 “TransMAX/MIN” vs PT(chgjet#1) • Plots shows data on the “transMAX/MIN” <Nchg> and “transMAX/MIN” <PTsum> vs PT(chgjet#1). The solid (open) points are the Min-Bias (JET20) data. • The data are compared with the QCD Monte-Carlo predictions of HERWIG 6.4 (CTEQ5L, PT(hard) > 3 GeV/c) and two tuned versions of PYTHIA 6.206 (CTEQ5L, PT(hard) > 0). <Nchg> <PTsum>

  35. Tuned PYTHIA 6.206 vs HERWIG 6.4 “TransSUM/DIF” vs PT(chgjet#1) • Plots shows data on the “transSUM/DIF” <Nchg> and “transSUM/DIF” <PTsum> vs PT(chgjet#1). The solid (open) points are the Min-Bias (JET20) data. • The data are compared with the QCD Monte-Carlo predictions of HERWIG 6.4 (CTEQ5L, PT(hard) > 3 GeV/c) and two tuned versions of PYTHIA 6.206 (CTEQ5L, PT(hard) > 0). <Nchg> <PTsum>

  36. Max/min 90o cones • Of the 2 cones at 90o (in the cone analysis), define the one with the greater energy as max and the lesser as min • Max cone increases as lead jet ET increases; min cone stays constant at a level similar to that found in minimum bias events at 1800 GeV • Both Herwig and Pythia provide good agreement for the min cone; Herwig provides better agreement for the max cone, but tuning of Pythia parameters does improve level of agreement with the max cone

  37. Alternative way of presenting • Of the 2 cones at 90o, define the one with the greater energy as max and the lesser as min • Max cone increases as lead jet ET increases; min cone stays constant at a level similar to that found in minimum bias events at 1800 GeV • Herwig agrees well with the data without any tuning

  38. Alternative comparisons with Pythia • Pythia parameters can be tuned to give a better fit to jet and min bias data at 1800 GeV • use pto (regularization scale for multiple parton scattering) of 2.0 GeV rather than 2.3 GeV • use varying impact parameters option in Pythia for underlying event generation • harder events->smaller impact parameter

  39. Transverse Regions vs Transverse Cones • Multiply by ratio of the areas: Max=(2.1 GeV/c)(1.36) = 2.9 GeV/c Min=(0.4 GeV/c)(1.36) = 0.5 GeV/c. • This comparison is only qualitative! 2.9 GeV/c 2.1 GeV/c 0.5 GeV/c 0 < PT(chgjet#1) < 50 GeV/c 0.4 GeV/c 50 < ET(jet#1) < 300 GeV/c Can study the “underlying event” over a wide range!

  40. Another approach • Define Swiss cheese as the sum of track pT values in the central rapidity region subtracting off the momenta of the 2 (or 3) leading jets Both MCs agree with the data with the 3 leading jets subtracted; Herwig agrees better when the 2 leading jets only are subtracted

  41. Try same comparisons at 630 GeV • Good agreement of data with MC at 630 GeV Swiss cheese

  42. Comparisons to minimum bias events at 1800 and 630 GeV • Best fits to jet and min bias data at 1800 are for pto (cutoff scale for double-parton scattering) = 2.0 GeV • default Pythia value is 2.3 GeV Best fits to jet and min bias data at 630 GeV are for pt0 = 1.4 GeV Pythia default is 1.9 GeV; so stronger center of mass dependence in data

  43. Jet Production in Run 2 For Run 2b potential, see www.pa.msu.edu/~huston/run2btdr/tdr.ps Jets will be measured with the kT clustering algorithm as well as with improved cone clustering models.

  44. Measurements will extend to forward regions • Measurements in the forward region are crucial; a pdf explanation covers both regions; presumably new physics is central

  45. CDF Photons in Run 1B • Deviations from predictions of NLO QCD observed at both 1800 and 630 GeV • steeper slope at low pT • normalization problem at high pT at 1800 GeV

  46. Results consistent with those from D0 and UA2

  47. What’s the cause? • pdfs don’t appear to be the answer can cause shape change by suitable choice of factorization and renormalization scales

  48. What’s the cause? One possibility is the effect of soft gluon initial state radiation (see kT Effects in Direct-Photon Production, PRD59 (1999) 074007)

  49. Photon reach in Run 2a • Can direct photon production be used to probe the high x gluon and look for hj-like behavior?

  50. No

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