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F 2 bb from muon+jet final states at Z EUS

F 2 bb from muon+jet final states at Z EUS. B. Kahle, DESY Hamburg. Introduction Beauty measurements Beauty contribution to F 2 Summary and Conclusions. Motivation.

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F 2 bb from muon+jet final states at Z EUS

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  1. F2bb from muon+jet final states at ZEUS B. Kahle, DESY Hamburg Introduction Beauty measurements Beauty contribution to F2 Summary and Conclusions

  2. Motivation • Heavy flavour production in DIS is a test of pQCD providing an additional hard scale M to the momentum transfer of the boson Q and pt • Beauty contribution to F2 is directly sensitive to the gluon distribution in the proton • Beauty production is of increasing interest for higher energies -> LHC H / Z HERA LHC, e.g. HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  3. Beauty contribution to the proton structure function F2 ~negligible HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  4. Heavy Flavour production mechanism Kinematic variables: Q2 = -q 2photon virtuality, squared momentum transfer x = Bjorken scaling variable, for Q2>>(2mQ)2: momentum fraction of p constituent Multiple scales:mb~ 5 GeV ptb~ typically few GeV Q 2> 1 GeV 2 in DIS ~ Dominant process in ep-collisions:Boson-Gluon-Fusion b b • Kinematic regime: • Deep inelastic scattering (DIS): Q2 > 1GeV2 different pQCD approaches good testing ground for pQCD HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  5. pQCD approximations • Massive scheme: • b massive • neglects [as ln (Q2/mb2)]n • scale mb ,pt • b produced perturbatively (not part of the Proton or Photon) • Massless scheme: • b massless • resumes [as ln (Q2/mb2)]n • scale: Q2, pt • b also in Proton and Photon • Variable flavour number scheme (VFNS): • massive at small Q2 • massless at large Q2 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  6. Beauty identification Jet axis m e p e Process : ptrel method: ptrel is the momentum of the muon transverse to the axis of the associated jet (including the muon) ptrel spectrum is harder for b than for c statistical separation using MC c2 fit of b MC against c+lf MC to the data in ptrel resulting beauty fraction of about 21% scale Rapgap-b MC up by a factor 2.49 ptrel HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  7. Cross section Beauty cross section for the DIS process: Cuts on MCtrue quantities: Q 2 > 4 GeV2 0.05 < y < 0.7 Et,jet > 5 GeV -2 > ηjet > 2.5 pt,µ > 1.5 GeV -1.6 > ηµ Data: σbb= 77.1 ± 7.8 (stat.) ± 9.6(sys.) pb 14.9 MC (LO+PS): σbb= 31.0 pb lab NLO (HVQDIS): σbb = 32.9 ± 3.3 (sys.) pb • R,F2= pt2+4mb2 (simultaneous variation: factor 1/4 to 4) • mb= 4.75 GeV (variation: 4.5 GeV to 5 GeV) • Peterson frag. function = 0.0035 • Proton parton distribution: CTEQ5F4 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  8. Cross sections in pt and h hm ptm hjet ptjet HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  9. Cross sections in Q2 and Q2x Q2 Q2x (plot 1) Q2x (plot 3) Q2x (plot 2) HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  10. Calculation of F2bb = beauty contribution to F2 Cross section calculated using hvqdis(CTEQ5F4) for a tiny bin around (x,Q2) „Reduced cross section“ is defined as: Expected to be compatible with calculations by Riemersma et al. used for F2cc Neglecting the small contribution from FL, the reduced cross section is equal to F2: neglected HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  11. F2bb measurement The reduced cross section for data is the reduced cross section of the NLO multiplied by the ratio of data to NLO in a x,Q2 bin: Cross section for NLO using hvqdis with same settings as for (but requiring SL decay to m and jet) H1 uses the impact parameter method to measure F2bb and F2cc with an inclusive charm and beauty sample of 57pb-1: H1 Collab., A. Aktas et al., Eur. Phys. J. C45 (2006) 23-33 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  12. Kinematic plane (ZEUS) Q2x plot 3 Q2x plot 2 Q2x plot 1 03/04 data (x,Q2) values chosen for F2bb to compare with H1‘s results HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  13. F2bb at ZEUS and H1 ZEUS data lie above H1 data but compatible within errors. HVQDIS+CTEQ5F4 agrees with similar predictions by H1 ZEUS: 39 pb-1 H1: 57.4 pb-1 Theory predictions except HVQDIS+CTEQ5F4 provided by P.D.Thompson, hep-ph/0703103 ZEUS data point at Q2=200GeV2; x=0.13 is shifted to lower x value to be separated from the H1 point HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  14. F2bb vs. Q2 Same ZEUS data. Some points are recalculated for other values of x to be comparable with H1 data and theory curves. ZEUS data are derived using HVQDIS+CTEQ5F4 and should strictly compared only with this curve. For comparison with other curves, model dependencies have to be taken into account. Some ZEUS data point are shifted to higher Q2 values to be separated from the H1 point HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  15. PDF Schemes and Parameters Theory predictions except HVQDIS+CTEQ5F4 provided by P.D.Thompson, hep-ph/0703103 HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  16. F2bb at ZEUS and H1 Same plot as before, but with additional theory curves. ZEUS: 39 pb-1 H1: 57.4 pb-1 Theory predictions except HVQDIS+CTEQ5F4 provided by P.D.Thompson, hep-ph/0703103 ZEUS data point at Q2=200GeV2; x=0.13 is shifted to lower x value to be separated from the H1 point HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  17. Summary and Outlook • First measurement of F2bb at ZEUS (39 pb-1), ~10 times more data to come -> much reduced errors • Results agree with H1’s using a very different method to obtain F2bb but similar uncertainties (both statistical and systematical) • NLO predictions agree with data within large spread. Questions to this meeting: What are the reasons for the large NLO spread? Does this affect the PDF extraction from inclusive F2? HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  18. BACKUP HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  19. NLO calculations The calculation of the NLO QCD visible cross section predictions proceeds in three steps: • HVQDIS(B.Harris, J.Smith, hep-ph/9503484): *gbb, *gbbg, *qbbq, etc.(pointlike only) usingCTEQ5F4(FFNS) PDF • Fragmentation of the b-quark into a B-meson (Peterson function with =0.0035) • Semileptonic decay of the B-meson (Muon momentum spectrum extracted from RAPGAP, including primary and secondary muons) HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  20. CTEQ5F4 with different scales F2bb using different scales for CTEQ5F4: Q2 Q2+4M2 (M=4.5GeV) Q2+4M2 (M=4.75 GeV) large differences at low Q2 for different masses HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  21. Extrapolation to full phase-space Extrapolation factor excluding branching fraction to m of 0.3924 Extrapolation factor includes ptb and hb spectrum, fragmentation, and decay kinematics (jet and m) Similar to extrapolations for F2cc HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

  22. Inclusive lifetime tags H1 mirrored inclusive DIS most significant impact parameter S1 charm 2nd most significant impact parameter S2 beauty HERA and the LHC - F2bb at ZEUS - Benjamin Kahle

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