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Heavy Flavor Production at HERA

Heavy Flavor Production at HERA. - Chapter 6 in arXiv: 0805.3334. Xin Dong. Introduction Measurements of HF production at HERA Production cross sections Structure functions HF production at hadron collider Summary. p. c. p. c. Heavy Production in ep and pp.

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Heavy Flavor Production at HERA

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  1. Heavy Flavor Production at HERA - Chapter 6 in arXiv: 0805.3334 Xin Dong • Introduction • Measurements of HF production at HERA • Production cross sections • Structure functions • HF production at hadron collider • Summary

  2. p c p c Heavy Production in ep and pp LO direct production Heavy flavors are sensitive probes to the initial gluon distributions!

  3. Production Cross Section ep pp QCD, MQ, Q2 pT MQ >>QCD in principle, amenable to pQCD calculations. Treatment of heavy quarks in pQCD calculations: Q2>>MQ2 heavy quarks are massless heavy quarks are massive Q2 ~ MQ2

  4. Kinematics Ee, Ee’ :incident positron and scattered positron energy e’ : polar angle of scattered positron x: Bjorken x of photon xg: longitudinal momentum fraction of gluon in proton

  5. Charm Reconstruction at HERA D* STAR 2009 p+p 200 GeV

  6. D* Production Cross Section in DIS ZM-VFNS: massless charm Not appropriate at low Q2 HVQDIS: massive charm Not correct at high Q2 CASCADE: kt factorization Insteresting: HVQDIS agrees with data better at high Q2!

  7. D*-jet-jet production D*-jet-jet cross section • Angular correlation • Generally agree with NLO QCD • some room to improve in theory • Hint of high order corrections

  8. Photon-gluon fusion processes  = 180o

  9. Charm Structure Function epeccX *gcc *cc probe gluon/charm PDFs NLO QCD - Extracted from the PDF based on the NLO QCD fit to F2

  10. HF in Photoproduction D* - jet angular correlation x xg x1, direct process x<1, resolved process   Quasi real photon (Q2~0) Expect pQCD to be applied over the full phase space A good pQCD test - check whether need for higher order terms. Data/theory comparison indicates some inadequacies of the theory.

  11. HF Production with Vertex Detector Pointing resolution (H1 vertex detector) Significance of signed 2D impact parameter (normalized by the resolution)

  12. Charm and Bottom Structure Functions

  13. HF Production in Hadron Collisions At RHIC (mid-rapidity), dominated by the gluon-gluon fusion x range ~ 0.005 - 0.1 gluon splitting flavor excitation LO NLO

  14. Predictive Power for Total Cross Section CTEQ6M =2mc =mc =0.5mc 10-3 10-2 10-1 10-3 10-2 10-1 PDFs extracted from inclusive DIS and inclusive jet data. R. Vogt, LBL Seminar Important scales in calculating the total charm cross section: mc,  • Drastic change of the gluon density function at low Q2 Strong dependence on s • Large uncertainty in predicted total charm cross section (at RHIC)

  15. Fixed-Order-Next-to-Leading-Logarithm - FONLL Treat the charm quark as light quarks; should be reliable at pT>>mc CDF p+p 1.96 TeV STAR p+p 200 GeV

  16. Summary Heavy flavors are sensitive probes to gluon distributions in nucleon/nucleus. Measurements at HERA generally agree with NLO QCD calculations. However larger (x,Q2) region need to be explored and with high precision to constrain the gluon (spin-dependent) density distributions. More complicated for HF production in hadron collisions. Precision measurements are needed for pQCD test.

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