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Heavy Flavour Content of the Proton

Heavy Flavour Content of the Proton. Paul Thompson University of Birmingham. for the H1 & ZEUS Collaborations. Motivation Experimental Techniques charm and beauty cross sections in DIS. Available Data.

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Heavy Flavour Content of the Proton

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  1. Heavy Flavour Content of the Proton Paul Thompson University of Birmingham for the H1 & ZEUS Collaborations • Motivation • Experimental Techniques • charm and beauty cross sections in DIS

  2. Available Data • In total ~500pb-1 of high energy data collected per experiment • luminosity upgrade in 2001 • detectors adjusted • ZEUS: new micro vertex detector Many preliminary analyses on full HERA II data Working on final publication and combination of results

  3. Production of Heavy Quarks Predominantly via boson gluon fusion Test of perturbative QCD: multi-scale problem (Q2, mb2, pt2) Directly sensitive to gluon density in the proton (PDFs) F2bb measurements at high Q2 important for LHC e.g. bb->H Heavy quark contribution to structure function

  4. Predictions for Heavy Quark Production Number of theoretical approaches: Massless (Zero Mass), massive (Fixed Flavour) and general mass (GM) flavour number schemes. QCD Calculations: Fixed order NLO(as2), massive FFNS (HVQDIS) GM-VFNS PDFs MSTW08 to NLO (as2) and NNLO CTEQ 6.6 to NLO (as) Monte-Carlo: LO (s)+Parton shower: Collinear factorisation, DGLAP (RAPGAP) KT factorisation, CCFM (CASCADE)

  5. Contribution to Cross Section HERA I result: • fraction of total DIS cross section from charm and beauty • large charm fraction (~30%) • small beauty fraction ~% (lower at low Q2) • mass thresholds visible • reasonable description by QCD

  6. Tagging Heavy Quarks (c) resonances D*, D+, D0,… Full HERA II statistics (~350pb-1) resonances and decay length tagging using vertex detectors

  7. Tagging Heavy Quarks (b) Beauty quarks rarely produced, use properties of beauty hadrons: • semileptonic decays(m,e) • mass - transverse momentum ptrel relative to jet axis • lifetime (vertex detectors) - reconstrucion of a secondary vertex - impact parameter d

  8. D* Cross Section H1 prelim-08-072 H1 prelim-08-074 • good description by NLO calculation (HVQDIS) in wide Q2 range • Also at large Q2, where massive approach not expected to be appropriate

  9. D* Cross Section D* • differential cross sections of several D mesons measured • reasonably described by NLO QCD (HVQDIS) • double differential in x and Q2 allows extraction of F2cc H1 prelim-08-072 D0 D+ ZEUS-prel-07-034 ZEUS-prel-07-009

  10. D* Fragmentation

  11. D* Fragmentation • RAPGAP MC: pT,jet> 3 GeV, parameters consistent with e+e- • no jet sample (low photon gluon COM) needs harder frag. • Similar story for HVQDIS DESY-08-080

  12. Charm and Beauty Cross Section • combine pTmiss||m, pTrel and impact parameter distributions • use 3D fit to decompose into beauty, charm and light flavour • Q2 > 20 GeV2, 0.01< y < 0.7, PTm > 1.5 GeV, -1.6 < hm < 2.3 • c and b cross sections described by NLO (HVQDIS) ZEUS-prel-08-007

  13. Charm and Beauty Cross Section • beauty tends to be above NLO QCD at low Q2 • may be measured double differentially in x, Q2 and extrapolated to full phase space to compare F2cc, F2bb

  14. Inclusive Analysis (lifetime) • Inclusive analysis: use all tracks with hits in silicon detector (pt > 0.3 GeV) • H1 CST rebuilt to account for HERA II beamline • Precise determination of impact parameter in transverse plane Signed impact parameter 

  15. Inclusive Analysis (lifetime) Signed Impact parameter Significance = d/s(d) Charmandbeautyasymmetric due to lifetime Light flavours mostly symmetric resolution lifetime H1 prelim-08-173

  16. Neural Network • Improve separation power: use neural network for >= 3 tracks • Inputs: S1, S2, S3, SL, track pt, number of (SV) tracks • Sign given by S1. Subtract –’ve from +’ve to reduce syst. error

  17. Inclusive b Cross Section • comparison of different methods [acceptance] • - Inclusive (H1VTX) [>90%] • - m ptrel (ZEUS 03/04 m ) [20-35%] • - m ptrel + d (ZEUS 05 m) [25-50%] • ZEUS tend to be higher than H1 • generally described by NLO QCD (FFNS, GM-VFNS)

  18. Measurements of F2bb • Beauty structure function versus Q2 • NNLO predictions available • Differences between NLO and NNLO small except for Q2<(mb)2

  19. Inclusive Charm Cross Section • comparison of different methods [acceptance] • Inclusive (H1 HERA I II VTX) [>70%] • Mu ptrel+d (ZEUS HERA II m) [25-50%] • D* cross sections [20-70%] • different methods agree well • wealth of precise measurements • combine to improve precision

  20. Measurements of F2cc • Charm measurements span large range in Q2 and x • theory predictions have different inputs • -parton densities • -mass treatment • Differences for Q2<(2mc)2

  21. Conclusions • Wealth of new measurements of the heavy flavour content of the proton from HERA I and HERA II data. • Extraction of structure functions F2ccand F2bb allow comparison of many different measurement techniques. • Data are described by (N)NLO pQCD calculations. • Data help to constrain theory mass treatments and PDFs (in time for LHC!). • Final results with full HERA statistics expected soon!

  22. Back Up

  23. Scale Uncertainty (c)

  24. Scale Uncertainty (b)

  25. H1 Vertex Detector CentralSiliconTracker (30o <  < 150o) • Rebuilt to take into account HERA II beamline • Double layer double sided strips • Precise determination of impact parameter in transverse plane • Resolution of |δ| for hits in both layers: Signed impact parameter 

  26. D* Fragmentation

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