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Wolfram Zeuner/DESY on behalf of

Open Heavy Flavour Production at HERA. Wolfram Zeuner/DESY on behalf of . Introduction Selected Results from Charm - Photoproduction and DIS Charm Fragmentation Beauty - Photoproduction and DIS Summary . Open Heavy Flavour Production at HERA. Study c and b production

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Wolfram Zeuner/DESY on behalf of

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  1. Open Heavy Flavour Production at HERA Wolfram Zeuner/DESY on behalf of • Introduction • Selected Results from • Charm - Photoproduction and DIS • Charm Fragmentation • Beauty - Photoproduction and DIS • Summary

  2. Open Heavy Flavour Production at HERA • Study c and b production • Hard scale from mQ tests of pQCD • Access to gluon in proton and photon • Study non-perturbative effects • as fragmentation LO (s) Direct BGF Resolved photon + ... In higher order only the sum of all contributions is well defined Flavour excitations

  3. Kinematic Variables • ep collisions: Ee=27.5 GeV, Ep=820/920 GeV • HERA produces boson proton interactions Luminosities e-p:  15 pb-1 e+p: 120 pb-1 • Kinematic regions • Photoproduction (p) : Q20 • Deep Inelastic Scattering (DIS): 1Q2  5·104 GeV2

  4. Calculations and Models Perturbative QCD 1. Fixed order NLO QCD (FO) calculations Heavy Quark produced only in hard scattering DIS: B. W. Harris, J. Smith, Phys. Rev D57, 2806 (1998) - HVQDIS MC p: Frixione et al.,Nucl. Phys. B454 (1997) 3 2. Resummed calculations in NLO (RS) Heavy Quark is an active flavour inside the proton and photon B. Kniehl et al. Z. Phys C76 (1997) 690; J. Binnewies et al., Z. Phys C76 (1997) 677; Phys. Rev. D58 (1998) 14014 M. Cacciari et al., Phys. Rev. D55 (1997) 2736; ibid 7134 3. Variable flavour numbers (VFNS), flavours are active depending on scale M.A.G. Aivaizis et al. Phys. Rev. D50 3102 (1994) (ACOT) • LO Monte Carlo Calculations – (BGF) • AROMA (direct only), HERWIG and PYTHIA (direct+resolved) • DGLAP evolution – (Q2 ordering) • CASCADE based on CCFM evolution – (angular ordering) Typical scales p: DIS:

  5. Open Charm Production • Charm tagging through D*± mesons 31350 ± 240 using M method • Other decays and mesons are used • semi leptonic electrons - via dE/dx

  6. ZEUS 96+97 Charm cross sections - D* and Ds in p • FO QCD (FMNR) • p: MRSG, : GRV-G HO • Thin: mc=1.5 GeV, R= mT= F/2 • Thick: mc=1.2 GeV, R= 0.5 mT • f(cD*)=0.235 (LEP) • Data more precise than prediction • Normalisation, low and par. dependent RS QCD (Kniehl et al.) p: CTEQ4M, mc=1.5 GeV, R= mT= F/2 • Problems to describe shape • Too low at high  • Sensitive to -PDF • Best with GS-G-HO, but u=c

  7. Charm Production in DIS Double differential D* production cross section • QCD predictions: bands (mc,c) : (1.3 GeV,0.35) - (1.5 GeV, 0.01) • HVQDIS - NLO DGLAP prediction too low for low pt and positive  • CASCADE - LO CCFM MC describes data better

  8. Assumptions • NLO FO calculation (BGF) • Neglect bound charm (2.5-4.5%) • Neglect • BR(c D*) = 0.222 - 0.233 from e+e- • Extrapolate to full phase space • in pT and h • Fragmentation effect on the • extrapolation is small Charm Production in DIS - • All measurements agree • Data described by NLO QCD • Strong scaling violations • Steep rise toward low x • Ratio grows towards • low x ( >25% for Q2  6.5 GeV2)

  9. Open Charm Production - The Gluon Density Distribution Reconstruct gluon momentum fraction xg from e and D* Extract xgg(xg,Q2) by unfolding differential D* cross sections using FO NLO calculations xgg(xg,Q2) xg Gluon parton density from D* in p and DIS agree with QCD fit to inclusive DIS cross section

  10. Unexpected observation Charm Production in DIS - D* • The ratio (e-p)/(e+p) rises towards • high Q2 and high x • Both cross sections are compatible • with NLO prediction within errors  More data needed

  11. Charm Fragmentation - Universal ? • Fragmentation fractions of excited D and Ds mesons • Strangeness production from • Ds   (K+ K-)  vs. D*D0  (K )  •  Strangeness suppression factor s of LUND model

  12. Charm Fragmentation - Universal ? • Production of vector mesons (D0) vs pseudoscalar mesons (D*) assume (D*±) = (D*0) PV= 0.546±0.045±0.028 ZEUS 0.57 ±0.05 OPAL 0.595 ±0.045 ALEPH D0 from D*± D0 not from D*± • No difference in charm fragmentation found between ep and e+e- collisions • All experimental results favour universality of charm fragmentation

  13. Jet Axis or Thrust Axis ptrel Lepton Jet Jet   >0 <0 Open Beauty Production High quark mass  pQCD, but cross section low b/ c 10-2 • B Tagging: • Semi-leptonic decays with a ptrel method - H1+ZEUS • Impact parameter method - H1 • using lifetime information - • Intercept of muons from semi-leptonic • decays in the transverse plane

  14. Beauty in Photoproduction H1 - Muon Analysis Combined likelihood fit to ptrel and  Combine with earlier ptrel measurement B fraction 27±3 % - from fit to MC • Predictions: • NLO (FMNR) 54 ±9 pb • AROMA (LO no resolved) 38 pb • CASCADE (LO CCFM-splitting) 66 pb All predictions significantly below data

  15. Beauty in Photoproduction • ZEUS electron analysis • Electrons identified by dE/dx of tracks Fitted b fraction: 14.7±3.8% - HERWIG predicts 16.2% Cross section by MC (LO) on the low side HERWIG: 8pb, Pythia: 18 pb, Cascade 20 pb

  16. Beauty in Photoproduction ZEUS Muon Analysis From fit: fb~30% • Pythia with b excitation describes data reasonably well • NLO ? – more data on tape to be analysed

  17. Beauty in DIS First observation of b production in DIS by H1; analysis like in p Sample: 168 events Combined fit in ptrel and  fb= 43±8% Predictions: NLO QCD:  = (11±2) pb LO MC - AROMA:  = 9 pb CASCADE:  = 15 pb

  18. Summary - Open Beauty Production at HERA Measured cross section exceeds NLO calculation in p and DIS • LO -Monte Carlo predictions are always on the low side • Quark excitation improves agreement in central region • CCFM improves agreement in central region • Forward region too low in all predictions

  19. SUMMARY • Large mass of c and b defines hard scale for pQCD • Charm - total cross sections predictable • p cross section higher than predicted by LO-MCs and NLO calc. at high  • DIS cross section higher than predicted at high , low x and low Q2 • Beauty Cross section measured in p and DIS • clearly underestimated by NLO predictions - surprising • NNLO Calculations and MCs are needed • Investigation of interactions with p-remnant (DIS) or -remnant (factorisation) • Need to investigate non-perturbative effects • Charm fragmentation - no difference seen between e+e- and ep • What comes next ? • HERA has been upgraded for high luminosity - 1fb-1 until 2006 • Detectors have been upgraded - higher sensitivity and efficiency • Precision measurements, QCD tests • and detailed investigations of the gluon in the proton, surprises not excluded

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