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heavy flavor production

heavy flavor production. Ulrich Heintz Boston University. disclaimers/acknowledgements. not a comprehensive review but selected results with concentration on b-production at the Tevatron not covered at all c-production results from e + e - collisions

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heavy flavor production

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  1. heavy flavor production Ulrich Heintz Boston University U. Heintz - PiC 2005

  2. disclaimers/acknowledgements • not a comprehensive review but selected results with concentration on b-production at the Tevatron • not covered at all • c-production • results from e+e- collisions • material from talks at Moriond, La Thuile, Beauty 2005 • thanks to D.Bauer, I.Belyaev, I.Bloch, M.D’Onofrio, M.Hildreth, V.Papadimitriou U. Heintz - PiC 2005

  3. why? • check our understanding of QCD • heavy flavor production at high energies checks perturbative QCD • extracting fundamental parameters of the standard model at hadron colliders requires deep understanding of QCD U. Heintz - PiC 2005

  4. b production at high energies • HERA (H1/ZEUS) 30/920 GeV • photoproduction Q2<1 GeV2 • hard scales: mb, pT • deep inelastic scattering Q2>1 GeV2 • hard scales: mb, pT, Q2 • Tevatron (D0/CDF) √s=1.96 TeV • hard scales: mb, pT • at least one hard scale  pQCD should work concentrate on Tevatron U. Heintz - PiC 2005

  5. b production at high energies DO Run I (PRL 84 (2000) 5478) CDF Run I (PRL 85 (2002) 5068) U. Heintz - PiC 2005

  6. DØ • excellent muon acceptance |η|<2 • excellent tracking coverage |η|<3 • (impact parameter trigger @L2) U. Heintz - PiC 2005

  7. CDF • excellent mass resolution • particle id: tof and dE/dx • impact parameter trigger @L2 U. Heintz - PiC 2005

  8. Tevatron performance • since June 2003 3-fold increase in • peak luminosity • integrated luminosity per week • total integrated luminosity • instantaneous luminosities above 1032cm-2s-1 • total integrated luminosity just reached 1 fb-1 • analyses shown use 40-300 pb-1 U. Heintz - PiC 2005

  9. b production at Tevatron • b production cross section at √s=1.96 TeV  50b • rate  few kHz at current luminosities • many developments in theory in recent years • full calculations to NLO • resummation of log(pT/mb) terms (fixed order NLO +NLL  FONLL) • substantial changes in fragmentation functions • new pdf’s leading order next to leading order U. Heintz - PiC 2005

  10. b cross section measurements • J/ and b-hadron production cross sections (CDF) • Inclusive b-jet cross section (CDF) • High pTcross section for -tagged jets (DØ) U. Heintz - PiC 2005

  11. b cross section using J/ (CDF) • use exclusive decays of b-hadrons to measure the b-production cross section • inclusive J/ cross section • fraction of J/ from decay of b-hadrons • b-hadron cross section for all pT U. Heintz - PiC 2005

  12. J/’s can originate from direct production decay of excited cc-states decay of b-hadrons dimuon trigger ¼ 300k J/ events mass resolution 15-20 MeV b cross section using J/ (CDF) U. Heintz - PiC 2005

  13. b cross section using J/ (CDF) • inclusive J/ cross section U. Heintz - PiC 2005

  14. b cross section using J/ (CDF) • long life time of b-hadrons • c ¼ 450 m • J/ decay vertex displaced • plot pseudo proper decay time x=Lxy m/pT in bins of pT of J/ • max likelihood fit for b-fraction fb = 9.4% fb = 33.7% U. Heintz - PiC 2005

  15. b cross section using J/ (CDF) • systematic error on b-fraction ¼ 3-13% U. Heintz - PiC 2005

  16. b cross section using J/ (CDF) • total inclusive b-hadron cross section Ldt¼ 40 pb-1 PRD 71, 032001 (2005) comparison with Run I B+ cross section Run II scaled for B+ fragmentation, |y|<1 U. Heintz - PiC 2005

  17. high-pT b-jet cross section (CDF) • reconstruct b-decay vertex using displaced tracks in jet • Rjet=0.7, |yjet|<0.7 U. Heintz - PiC 2005

  18. high-pT b-jet cross section (CDF) • determine b-fraction of tagged jets in bins of jet pT using mass of particles that point to secondary vertex U. Heintz - PiC 2005

  19. high-pT b-jet cross section (CDF) • b-jet cross section for 38<pT<400 GeV • L dt = 300 pb-1 U. Heintz - PiC 2005

  20. high pT-tagged jet cross section (DØ) • first step to b-production cross section • jet with  in cone • Ldt = 300 pb-1 • Rjet=0.5, |yjet|<0.5 • 4660 -tagged jets • PYTHIA:  55% of all -tagged jets from heavy flavor (b,c) U. Heintz - PiC 2005

  21. high pT-tagged jet cross section (DØ) • unsmear detector resolution NLO: Z. Nagy, Phys. Rev. D 68, 094002 U. Heintz - PiC 2005

  22. what changed? • long-standing “discrepancies” between predicted and measured cross sections seem resolved • better theory: • sum terms with log(pT/mb) (FONLL) • e.g. Cacciari, Frixione,Mangano, Nason, Ridolfi, JHEP 0407 (2004) 033 • better understanding of fragmentation functions • better estimate of theory errors (upward!) • better parton distributions: • add more gluons • better experimental observables: • not b-quarks but b-hadrons U. Heintz - PiC 2005

  23. quarkonia production • slightly different theoretical context • non-relativistic QCD (NRQCD) • Lepage et al., PRD 46 4052 (1992) • production described by short distance cross sections and nonperturbative matrix elements for evolution to quarkonium state. • color octet modes required on top of color singlet to describe production (demonstrated by CDF in Run I) • results: • DØ: Υ(1s) production, Υµµ final state • CDF: prompt J/ polarization U. Heintz - PiC 2005

  24. Y(1S) production (DØ) • test boundary between perturbative and non-perturbative QCD • perturbative color singlet production suppressed by s • color evaporation (soft gluons carry away color/spin  non-perturbative) • perturbative color octet production can reproduce high pT region • V.A. Khoze , A.D. Martin, M.G. Ryskin, W.J. Stirling, hep-ph/0410020 • resum logs to address low pT region • E.L. Berger, J.Qiu, Y.Wang, Phys Rev D 71 034007 (2005) color octet process color singlet process U. Heintz - PiC 2005

  25. Y(1S) production (DØ) • unlike charmonium, all bb-states are produced directly • 50% of Y(1S) from decay of other bb-states U. Heintz - PiC 2005

  26. Y(1S) production (DØ) • fix mass splittings and relative widths in fit • 5 free parameters: • m(1S), (1S), n(1S), n(2S), n(3S) all three: 4 GeV < pT(Y) < 6 GeV |y(Y)|<0.6 0.6<|y(Y)|<1.2 1.2<|y(Y)|<1.8 U. Heintz - PiC 2005

  27. Y(1S) production (DØ) • little variation in the shape of the cross section as a function of rapidity • reasonable agreement with calculations by Berger et al, hep-ph/0411026 Ldt = 159 pb-1 hep-ex/0502030, PRL 94 232001 (2005) U. Heintz - PiC 2005

  28. prompt J/ polarization (CDF) • large prompt J/ cross section (Run I) • color octet mechanism Braaten/Fleming PRL 74 3327 (1995) • transversely polarized J/ at large pT transverse alignment (symmetric decays) longitudinal alignment (asymmetric decays) U. Heintz - PiC 2005

  29. contributing processes: g fusion resolved  contributes to photoproduction suppressed at high Q2 1999-2000 H1 e§ p (72 pb-1) ZEUS e+ p (50 pb-1) HERA 28 GeV 920 GeV U. Heintz - PiC 2005

  30. HERA •  + dijet • photoproduction • Q2<1 GeV2 • H1: • b-identification • large mass • pT of  relative to jet • long life time • impact parameter of  • vis(epebbXejjX)=38.4§3.4(stat)§5.4(syst) pb • prediction: 23.8-5.1+7.4 GeV U. Heintz - PiC 2005

  31. HERA •  + jet • deep inelastic scattering • 2 GeV2 < Q2 < 100 GeV2 • vis(epebbXejX)=16.3§2.0(stat)§2.3(syst) pb • prediction: 9.0-1.6+2.6 GeV U. Heintz - PiC 2005

  32. HERA • see discrepancy at low pT and high  U. Heintz - PiC 2005

  33. HERA • discrepancy at high  also seen in ZEUS data • ZEUS • vis(epebbXejX)=40.9§5.7(stat)-4.4+6.0(syst) pb • prediction: 20.6-2.2+3.1 GeV hep-ex/0405069 hep-ex/0502010 U. Heintz - PiC 2005

  34. conclusions • b production at the Tevatron • finally NLO QCD and data agree • better theory calculation: • FONLL + fragmentation functions + pdf’s • well-defined observables • quarkonium production • Y(1S) production agrees with pQCD + resummation predictions • J/ is not transversely polarized as expected by color octet production • b production at HERA • pQCD predictions are ¼ 2  low • discrepancies at low pT and high  U. Heintz - PiC 2005

  35. Thank you U. Heintz - PiC 2005

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