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Diffractive partons from perturbative QCD

This study replaces Regge factorization with pQCD Collinear factorization and explores the modifications needed in the HERA regime, including an inhomogeneous term in DGLAP evolution, direct charm contribution, and a twist-4 FLD component. The analysis provides a good description of DDIS data from H1 and ZEUS experiments and presents universal diffractive partons with smaller diffractive gluon contributions.

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Diffractive partons from perturbative QCD

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  1. Diffractive partons from perturbative QCD Alan Martin, Misha Ryskin and Graeme Watt Conventionally DDIS analyses use two levels of factorisation - collinear factorization and Regge factorization We replace Regge factorization by pQCD Collinear factorization, which holds asymptotically, needs modification in the HERA regime: -- inhomogeneous term in DGLAP evolution -- direct charm contribution -- twist-4 FLD component We present universal diffractive partons Alan Martin, DIS05 Madison,April 2005

  2. factorization proved for DDIS (Collins), but important modifications in the HERA regime

  3. H1 Large rapidity gap selection: MY<1.6 GeV and |t|<1 GeV2 H1 LPS proton selection: MY= mp extrapolated to |t|<1 GeV2 Good agreement between two methods and two experiments Data well described by H1 QCD fit to LRG data M.Kapishin, ICHEP04, Beijing

  4. see Laycock

  5. x=0.18 b=0.67

  6. lots of gluons at high b, theoretically puzzling from a perturbative viewpoint

  7. H1 NLO fits to • H1 LRG data • ZEUS MX data see Laycock

  8. H1 NLO fits to • H1 LRG data • ZEUS MX data see Laycock

  9. Hint of problem with Regge factorisation assumption assumes Pomeron ~ hadron of size R Regge factn occurs in non-pert region m<m0, where m~1/R but aP(0)~1.2 from DDIS > aP(0)~1.08 from soft data  small-size component from pQCD domain with larger aP(0) MRW study impact of applying pQCD to DDIS find DDIS factorization OK asymptotically, but important modifications in HERA (subasymptotic) regime

  10. rapidity gap

  11. given by pQCD

  12. m2 fP  flux does not behave as 1/m2 convergence decreases as xP decreases

  13. inclusion of the inhomogeneous term makes gP smaller gP inhomog. term xP=0.003 Q2=15 GeV2

  14. In practice, more convenient to solve standard DGLAP for each m starting from its own scale m (provided m>Q0). Then to integrate over m. m2

  15. dm2 m2 input forms: first try: assume xg ~ x -l following Wusthoff, BEKW loosely based parametrizations on such forms

  16. Fit to ZEUS and H1 diffractive DIS (prelim.) data xg = x -l

  17. xg = x -l gD SD ZEUS l=0.22 H1 l=0.13 combn l=0.17 H1 2002 fit use as=0.1085 cf. 0.1187(PDG) H1 have steeper Q2 dep. of S, hence larger g. Also no twist-4 FL

  18. but one of the HERA surprises…. global partons at g: valence-like S: Pomeron-like whereas expect lg ~ lS ~ 0.1 (xg ~ x –lg xS ~ x –lS )

  19. need to introduce Pomeron made of col. singlet qq pair Pomeron made of two gluons as well as Now Pomeron flux factors depend on Sp as well as gp

  20. dm2 m2 input forms: use MRST/CTEQ partons

  21. gD SD Fit with qq as well as gg Pomeron Uses MRST gp and Sp to calculate Pomeron flux factors v.good fit

  22. diffractive charm production constrains gluon direct contribution from gPom add separately. No evolution and no DDIS factorization

  23. the description of ZEUS diffractive charm production from gPom direct

  24. The corresponding MRW fit to the ZEUS LPS data  and H1 (prelim.) data

  25. MRW 2005 ZEUS LPS, charm, MX MRW 2005 ZEUS LPS, charm, H1 H1 fit 2002 MRW 2004 ZEUS LPS,MX, H1 MRW 20042005 parametrize bgP in DIS scheme then transform to MSbar

  26. H1 MRW CDF dijet data g* rapidity gap survival prob.

  27. Conclusions Analysis of DDIS, which goes beyond collinear + Regge factn Regge factorization replaced by pQCD --need quark-antiquark Pomeron, in addition to two-gluon Pomeron --the input forms of the Pomeron PDFs given by QCD diagrams Collinear DDIS factorization modified in HERA regime: --inhomogeneous DGLAP evolution  smaller gPom Good description of H1, ZEUS DDIS data We obtain universal diffractive partons --diffractive gluon considerably smaller than that of H1 fit --for hadron-hadron diffraction, must include rap. gap survival probability Moreover---the diffractive fit allows an estimate of the absorptive corrections in global DIS fit

  28. I I I P P P Contribution of diffractive F2 to inclusive F2 Apply the AGK cutting rules to contrib. AGK in QCD: Bartels & Ryskin Im Tel ~ stot DF2abs ~ - F2D negative (~Glauber shadowing)

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