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H1 and ZEUS R esults on B eauty P roduction   

H1 and ZEUS R esults on B eauty P roduction   . Isabell-Alissandra Melzer-Pellmann DESY Hamburg, ZEUS XXXIXth Rencontres de Moriond QCD and High E nergy H adronic Interactions March 28th - April 4th, 2004. Outline. Introduction and Theory

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H1 and ZEUS R esults on B eauty P roduction   

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  1. H1 and ZEUS Results on Beauty Production    Isabell-Alissandra Melzer-Pellmann DESY Hamburg, ZEUS XXXIXth Rencontres de Moriond QCD andHigh Energy HadronicInteractions March 28th -April 4th, 2004

  2. Outline • Introduction and Theory • Measurement techniques and Results (gP and DIS) • Jets + m • D*m correlations • Summary and Outlook

  3. Introduction: HERA p e Maximum centre of mass energies: s = 300 GeV (1992-1997) s = 318 GeV (1998-2000) Luminosity (1996-2000): e+p scattering: L  100 pb-1 e-p scattering: L  15 pb-1

  4. Theory:Beauty production at HERA • Driven by gluons in the proton • Kinematic regions dependent on the virtuality of the photon Q2: • Photoproduction (gP): Q2 < 1GeV2 • Hard scales: mb, pT Deep inelastic scattering (DIS): Q2 > 1GeV2 • Hard scales: mb, Q2, pT b b • Always more than one hard scale for as available • perturbative QCD should work…

  5. Theory:Description in pQCD Factorisation: Photon structure  Matrix element  Proton structure Photon structure: Role of resolved photons in beauty production? • QCD models • compared to data: • LO O(as) + parton shower: • Pythia MC (DGLAP) • Cascade MC (CCFM) • NLO O(as2) : • gP: FMNR • DIS: HVQDIS Hard ME Proton structure: Test pQCD approximation for gluon radiations: DGLAP, BFKL, CCFM

  6. Measurement technique:B -> mjjX Large B mass: A pT of m relative to the closest Jet is larger Large B lifetime: Am impact parameter d H1 gP (prel.): Combined max Likelihood fit (d, pT ): fb=30.72.5 % rel

  7. Results: B -> mjjX in Photoproduction Pseudorapidity • NLO is in good agreement with data • H1 slightly higher than ZEUS (agreement within errors)

  8. gP: Comparison of NLO QCD and LO+PS NLO QCD as well as LO + Parton shower MC describe the data reasonably well (MC below data for high hm and high pT)

  9. gP: Comparison NLO QCD and LO+PS for xg jets • tool to measure photon-gluon • fusion (peak at xg =1) in • comparison to other contributions • (e.g. gluon-gluon fusion or higher • order diagrams (photon structure, • distributed over the whole range) jets NLO QCD: good description of data Pythia: good description (large contribution from flavour excitation at low xg ) Cascade: underestimates data at low xg (generation of these events via initial state radiation without using a parton density in the photon) jets jets

  10. Results: B -> mjX in DIS • Jet variables: • Jets in Breit frame: • + 2x P = 0 • : momentum of exchanged photon x: Bjorken x P: Proton momentum Space-like photon and proton collide head-on Jet variable: ZEUS : sep = (40.9  5.7stat-4.4 sys) pb NLO QCD (HVQDIS): sep = 20.6 –2.2 pb Cascade (CCFM): sep = 28 pb RAPGAP (DGLAP): sep = 14 pb +6.0 vis +3.1 vis vis vis Isabell-A. Melzer-Pellmann Moriond QCD, 28.3.-4.4.2004

  11. DIS: Results for DIS variables (Q2, log10(x)) DIS variables: NLO QCD and Cascade (CCFM) describe data reasonably well, Rapgap (DGLAP) underestimates cross sections. Data slightly higher than NLO QCD (2s) at small Q2 and at small x.

  12. DIS: Results for m variables (pT, hm) m m Variables: NLO QCD and Cascade (CCFM) describe data reasonably well, Rapgap (DGLAP) underestimates cross sections. Data slightly higher than NLO QCD (2s) at small pT. m

  13. Measurement technique:D*m correlations Beauty Charm Separation by angular and charge correlations: • DF 90°-180°, unlike charge DF 0°- 90°, unlike charge DF 90°- 180°, unlike charge DF 90°- 180°, like charge

  14. Results:D*m correlations like charge unlike charge ZEUS: H1: incl. data: sep = (380  120stat  130sys) pb incl. data: sep = (214  52stat -84 sys) pb vis vis +96 Visible cross sections for H1 and ZEUS agree within errors.

  15. Event display:D*m correlations m- m- ps p- p e+ ps K+ p- e+ K+ e+

  16. Summary:Beauty at HERA • H1 and ZEUS performed various measurements • in different kinematic regions: • NLO QCD is in general in good agreement with data in most phase space regions, small discrepancies in some regions have been identified: • gP: NLO QCD in good agreement for all regions, LO + PS models slightly below data for high hm and high pT • DIS: NLO QCD underestimates rate for high ET,jet, low Q2, low x, low pT and high hm. LO + PS models behave similar. m m Breit

  17. Outlook • HERA I has come close to the sleeping beauty… • measurements of beauty cross sections require more data to really judge agreement with pQCD • HERA II is prepared to • wake the sleeping beauty! • Expect factor 5 higher integrated luminosity • Detector upgrade (ZEUS: microvertex detector) • Improvements on trigger HERA II

  18. BACKUP

  19. Summary plot:Beauty at HERA Recent H1 and ZEUS results imply smaller discrepancy between data and NLO QCD in gP as well as in DIS. DIS gP

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