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Analysis of diffractive DIS and its implications

Analysis of diffractive DIS and its implications. 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?

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Analysis of diffractive DIS and its implications

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  1. Analysis of diffractive DIS and its implications 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? The future of forward Physics Manchester,December 2004

  2. MRW philosophy: trust theory, even if it hurts hadronparton transition Q2 0 ~1 GeV2 DGLAP evolution: parton creation Regge Absorption: parton recombination Diffractive DIS data provide the link via the AGK cutting rules

  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. x=0.18 b=0.67

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

  6. first, assume xg ~ x -l following Wusthoff, BEKW loosely based parametrizations on such forms

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

  8. xg = x -l gD SD ZEUS l=0.22 H1 l=0.13 Comb. l=0.17 H1 use as=0.1085 H1 have steeper Q2 dep. of S, hence larger g. Also no twist-4 FL

  9. but… g: valence-like S: Pomeron-like whereas expect lg ~ lS ~ 0.1 (xg ~ x –lg xS ~ x –lS )

  10. 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

  11. use MRST

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

  13. 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

  14. 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

  15. 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)

  16. Include ZEUS data for diffractive charm production in the analysis should constrain the gluon distrib. of the Pomeron recall perturbative xgD ~ (1-b)2 --take non-pert. xgD ~ b --parametrize xgD in DIS scheme, then transf to MSbar cf. MRST physical gluons and large ET Tevatron jets try lg = lS fit, with shifted scale

  17. (LPS) Note that b<0.5 diffractive charm ZEUS fit

  18. SD gD Our “simultaneous” fit to ZEUS LPS v.good ZEUS charm v.good + all DIS F2 v.poor too much gluon, F2abs too big but… LPS data v.limited, b<0.5

  19. SD gD Our “simultaneous” fit to All DDIS good ZEUS charm OK + All DIS F2 good

  20. Aliosha’s worry about MRW x=0.18 b=0.67

  21. 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

  22. Conclusions Diffractive DIS New pQCD description – integral over Pomeron size, 1/m Good description of combined (prelim.) H1, ZEUS diffractive data Need quark-antiquark 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 + reasonable fit to diff. charm 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)

  23. MRST-type parametrization Input ~ MRST2001

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

  25. Effective αIP(0) vs Q2 Diffractive cross section: Inclusive cross section according to optical theorem: Effective αIP(0): • lower than for inclusive cross section • consistent with soft IP at low Q2 • data suggest increase with Q2 • Regge factorization breaking • similar W dependence of diffractive and inclusive cross section: 2(αIPdiff-1) ≈αIPtot- 1 M.Kapishin, ICHEP04, Beijing

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