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Godparents: W. Wester, J. Dittman, G. Feild

Godparents: W. Wester, J. Dittman, G. Feild. The B cross section. Introduction NLO calculation Previous measurements Final RUN 1 CDF measurement New theoretical developments Low energy SUSY and the b cross section Conclusion. D. Bortoletto Todd Keaffaber’s Thesis. Heavy quark NLO.

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Godparents: W. Wester, J. Dittman, G. Feild

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  1. Godparents: W. Wester, J. Dittman, G. Feild

  2. The B cross section • Introduction • NLO calculation • Previous measurements • Final RUN 1 CDF measurement • New theoretical developments • Low energy SUSY and the b cross section • Conclusion D. Bortoletto Todd Keaffaber’s Thesis

  3. Heavy quark NLO • Calculations of heavy quark production in hadronic collisions follow the approach developed by Collins, Soper and Sterman: • Explicit calculation were done at NLO (O(s3)) by Nason, Dawson and Ellis (NDE), Mangano Nason and Ridolfi (MNR) Nason et al., Nucl., Phys. B327 (1989) 49, B335 (1990) 260 W. Beenakker et al., Nucl. Phys. B351 (1991) 507 M. Mangano et al., Nucl. Phys B373 (1992) 295

  4. Heavy quark NLO • Theoretical predictions are usually presented varying R and F in the range The largest cross section (2) corresponds to large F and smallR • The uncertainty due to the PDF is small due to the tighter constraints set by DIS and HERA data (12-20%). • The mass of the b quark is varied between In this range the cross section can change by about 10%

  5. 20GeV 10GeV 60GeV 40GeV 630GeV 1800GeV Heavy quark NLO • The largest uncertainty in the cross section determination is the scale uncertainty which is sensitive to higher order corrections.

  6. B+ K+ u u u Experimental Measurements • Hadron collider experiments historically studied the b-quark cross section • More recently the differential cross section has also been studied. • Measurements have been performed using different data sets with electrons or muons and/or jets in the final state: • Inclusive decays e/ • Muon+jets • J/

  7. B cross section measurements • The single b inclusive cross section has been measured at several energies: • 540 GeV by UA1 • 630 GeV by UA1, CDF and D0 • 1.8 TeV by CDF and D0 630 GeV 630 GeV

  8. Early CDF measurements 1.8 TeV

  9. B cross section measurements • Excellent agreement between experiments • Significant excess in the data 1800 GeV

  10. B cross section measurements • The experimental measurements find a cross section higher than the theoretical prediction by a factor 2-3 630 GeV 1800 GeV

  11. B cross section measurements • Ratio of the cross section • Reduced theoretical and experimental uncertainties

  12. D0-b Jet measurement • D0: b tagging jets using muons. • Require ET(Jet)>25GeV, and PT()>6GeV Agreement with theory upper band for pT>55 GeV

  13. Summary of the measurements

  14. B cross section • In Run 1A first measurement of the B cross section by CDF. (PRL 75, 1451 (1995))

  15. B cross section • Measurement confirms discrepancy between theory and experiments • CDF published

  16. Run 1 Measurement RUN 1A RUN 1 • L=19.30.7 pb-1 • Use the decays • Muons can be both in SVX and CTC • Require CMU muons • L=984 pb-1 • Use only the decay • Require muons in SVX to have more precise ct information • Require CMU muons

  17. Data Selection • Track quality cuts • 4 hits in at least 2 axial superlayers • 2 hits in at least 2 stereo superlayers • Rexit(Kaon)>110 cm • Muons: • All muons have CMU stub • Muon matching • 3 hits in the SVX • Primary vertex

  18. J/ reconstruction • J/ reconstruction • +- are vertex constrained • Run 1A: and • Run 1B and or

  19. Data Selection • B reconstruction • SVX information used if available for the kaon • +- K are vertex constrained • +- mass constraint to J/ mass

  20. Event yield • Event yield for Run 1 analysis

  21. Fitting method • The B meson cross section is determined using where • Mi and i mass and width from the kinematic fit • s=scale factor • b=slope of the background • w=fit mass range

  22. Event yield in PT bins • Event yield for Run 1 analysis divided in 4 pT bins

  23. Acceptance • The product of the acceptance and trigger efficiency was calculated with BGEN, QQ, QFL, DIMUTG using the MRST structure functions • The QCD-NLO MC was run with: • Results:

  24. Efficiency • Efficiencies that are not included in the MC acceptance were calculated using data • Efficiencies that are not equal in Run 1A and Run 1B are averaged and weighted by the luminosity

  25. Cross Section • The B meson cross section is determined using • Where: • N is the number of B mesons from a unbinned likelihood fit • pT is the width of the pT bin • L is the corrected integrated luminosity • A is the MC acceptance which included the trigger efficiency. •  is the reconstruction efficiency • B=BR(B+ J/K+)  BR(J/  +-)=(5.880.60) 10-5

  26. Luminosity Correction • The measured J/ cross section fell as a function of the instantaneous luminosity • We correct for this effect: Feild, Lewis CDF note 4769

  27. Systematic uncertainties • Fully correlated systematic uncertainties which do not depend on pT • Uncorrelated systematic uncertainties which depend on PT

  28. Differential Cross Section • The measured cross section is: • To compare with the theory we plot the results at

  29. Differential Cross Section • The cross section is higher than the theoretical NLO

  30. Total Cross Section • Replace the last bin of the differential cross section • CDF measures: PT>15GeV/c QCD NLO central value  1.2 b

  31. Heavy quark NLO • Shape are well described by perturbative QCD • Large discrepancy on the cross section measurement • Presence of higher order terms • Fragmentation effects • Intrinsic kT of partons • New physics • Fixed order calculation have terms • Which could be quite large for

  32. New Theoretical developments • Variable Flavor Number Scheme (VFN) • (F.I Olness, R.J. Scalise and Wu-Ki Tung hep-ph/9712494) • Hadronization of heavy quarks • Harder bB fragmentation (Colangelo-Nason) • 30% (40%) higher B cross section in the central (forward) region

  33. New Theoretical developments • Studies of the kT effect

  34. New Theoretical developments • Correlated b production seems to disfavor large kT effects.

  35. ….

  36. New Physics Hypothesis • Supersymmetry could make a substantial contribution to the observed b cross section • Berger, Tait, Wagner et al. have a model with intermediate mass gluinos that decay into b and sbottom • The contribution is large if

  37. New Physics Hypothesis • The new contribution peaks at • b quarks have  and  similar to QCD production • Authors claim that this scenario is not ruled out by current limits.

  38. Conclusion • Final run 1 measurement of the B cross section confirms discrepancy with QCD NLO predictions • CDF and D0 measurements on different data sets give consistent measurements of the b cross section • NLO calculations model the shape but under-estimate b production • Puzzle in b production is now emerging also at LEP and at HERA

  39. Prospects for Run II • B physics program at hadronic machines continues to be complementary to B-factories • All B species are produced • High production cross section • Higher luminosity will bring higher statistic but also systematic effects that will need to be investigated. • Higher statistic will allow: • To probe higher ET region • Investigate the possibility to study the b-fragmentation at the Tevatron • Correlation studies

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