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A QCD analysis of diffractive DIS and its effect on global DIS analyses

A QCD analysis of diffractive DIS and its effect on global DIS analyses. Alan Martin, Misha Ryskin and Graeme Watt. Diffractive DIS occurs at about 10-20% the rate of DIS How should we analyse DDIS data? How do we treat DDIS events in global analyses of DIS data?.

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A QCD analysis of diffractive DIS and its effect on global DIS analyses

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  1. A QCD analysis of diffractive DIS and its effect on global DIS analyses Alan Martin, Misha Ryskin and Graeme Watt • Diffractive DIS occurs at about 10-20% the rate of DIS • How should we analyse DDIS data? • How do we treat DDIS events in global analyses of DIS data? • are they in the input distributions? • or, do we allow for them in the DGLAP evolution? Workshop on Low x Physics PragueSeptember 2004

  2. higher twist ln Q2 Bartels,Ellis, Kowalski & Wusthoff base parametrization on these forms

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

  4. Pomeron made of two gluons Pomeron made of two sea quarks Now Pomeron flux factors depend on Sp as well as gp

  5. I P

  6. gD SD H1 have steeper Q2 dep. of S, and hence larger g. Also no twist-4 FL

  7. S2 ~ 0.3 to 0.1 small, large size val sea,g H1 MRW HERA g* Survival factors calc. from 2-ch eikonal model based on multi-Pom. exchange & s channel unitarity KKMR S2 ~ 1

  8. What is the impact of the diffractive DIS analysis on the global parton analyses to DIS and related data? We are ready to answer the question: are the DDIS data included in the DIS input ? or should they be allowed for in DIS DGLAP evol ? Moreover---the diffractive fit allows an estimate of the absorptive corrections in global DIS fit

  9. I I I I I P P 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) In pQCD, is a cut, not a pole Lipatov has a continuous no. of compts of different size, r~1/m For eachcompt., DGLAP evol. of F2D(b,Q2,m2) starts from m Q provided it is large enough

  10. (for x < 0.01)

  11. MRST-type parametrization Input ~ MRST2001

  12. % increase of gluon and sea due to absorptive corrections gluon sea quarks

  13. Good news: absorp. corr. remove need for –ve gluon But: still have valence-like gluon Pomeron-like sea quarks to hadrons: Regge xg, xS ~ x –l with lg = lS Suppose we impose lg = lS, very poor fit can get acceptable fit, but only if we shift scale in F2(x,Q2) from Q2 to Q2 + 1 GeV2 (mimicks power corrections)

  14. Need Q2  Q2+1 mimicks power corr. xg, xS  const

  15. Conclusions Diffractive DIS New pQCD description – integral over Pomeron size, 1/m Good description of combined (prelim.) H1, ZEUS diffractive data Need two-quark Pomeron, in addition to two-gluon Pomeron The input forms of the Pomeron PDFs given by QCD diagrams Pomerons PDFs different to previous determinations DIS + diffractive DIS • The above F2D analysis allows an estimate of the absorptive corr. to F2 • removes the need for a negative gluon Good simultaneous fit to DDIS + DIS data But gluon is still valence-like, sea Pomeron-like either non-pert. Pomeron does not couple to gluons or DGLAP frozen at low scales (~power corrections)

  16. I P • Diffractive DIS occurs at about 10-20% the rate of DIS • How should we analyse DDIS data? • Use pQCD for x , b, as well as Q2, dep. • Integrate over the size of the QCD Pomeron, 1/m • How do we treat DDIS events in global analyses of DIS data? • are they in the input distributions? • yes, partly m<Q0 • or, do we allow for them in the DGLAP evolution? • yes, partly m>Q0

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