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Diffractive dijets in photoproduction

Diffractive dijets in photoproduction. single differential cross sections. Shinji Kagawa on behalf of the ZEUS Collaboration. Diffractive dijets in photoproduction. Parton momenta in the Pomeron ( IP ): reconstructed by jets Dominant process: gluon-intiated process

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Diffractive dijets in photoproduction

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  1. Diffractive dijets in photoproduction single differential cross sections Shinji Kagawa on behalf of the ZEUS Collaboration Diffractive dijets in photoproduction

  2. Diffractive dijets in photoproduction Parton momenta in the Pomeron ( IP ): reconstructed by jets Dominant process: gluon-intiated process (e.g. boson gluon fusion)  Sensitive to the gluon content of the Pomeron zIPobs longitudinal momentum fraction of the IP taken by the dijet Direct process: total longitudinal momentum of  taken by the dijet Diffractive dijets in photoproduction

  3. The resolved  process in diffractive dijets in photoproduction Resolved  process: • exchanged photon: source of partons  like a hadron • similar to hadron - hadron collision • dominant process at low xobs xobs longitudinal momentum fraction of the  taken by the dijet Diffractive dijets in photoproduction

  4. Factorization breaking in pp collisions  • Possible mechanism of suppression: secondary interactions filling the rapidity gap.  Is there also a suppression of resolved  processes, which are supposedly similar to pp ? • pp collisions at TEVATRON:suppression of diffractive dijetsby a factor of approx. 10(factorization breaking) Diffractive dijets in photoproduction

  5. Suppression of resolved  processes at NLO • M.Klasen and G.Kramer made NLO calculations and compared them to H1 results. • No suppression at LO • At NLO, H1 data is well reproduced when the resolved part is suppressed by a factor of 0.34 • Only suppression at NLO ? Diffractive dijets in photoproduction

  6. Other kinematic variables dijet fraction of electron energy transferred X Direct process longitudinal momentum fraction of the proton transferred invariant mass of the system X dijet X • Reconstruction of jets • longitudinally-invariant kT algorithm Resolved process Diffractive dijets in photoproduction

  7. Kinematic range for measured cross sections • PHP: 0.20 < y < 0.85, Q2 < 1.0 GeV2 • Diffraction: xIP< 0.035 • Dijet: ETjet1(2) > 7.5(6.5) GeV 1.5 < jet1,2 (lab frame)< 2.0 Diffractive dijets in photoproduction

  8. Example event Large rapidity gap (max) characterizing diffractive events e (not detected) dijet Diffractive dijets in photoproduction

  9. Data sample and selection cuts ZEUS 9900 data (77.6 pb-1) Diffractive events selected by requiring (in the lab frame) • E < 1 GeV from pseudorapidity 45 (in the Forward Plug Calorimeter) • no cluster with E  0.4 GeV from pseudorapidity 34 (max cut in the Calorimeter) Large data sample: 10673 events • measurements possible up to high jet ET where NLO calculations are reliable Diffractive dijets in photoproduction

  10. Monte Carlo • RAPGAP version 3.00/00 (Hannes Jung) • Structure functions: GRV-G-LO (  ), H1-fit2 ( IP ) • Only Pomeron contribution generated (no Reggeon) Diffractive dijets in photoproduction

  11. Control plots (I) • MC: reweighted in zIPobs •   (direct) +   (resolved) • is fitted to data in xobs •   = 1.1 • MC has higher max than data •  largest systematic error Diffractive dijets in photoproduction

  12. Control plots (II) • jet1: highest ET jet • jets and MX are well described by MC Diffractive dijets in photoproduction

  13. Differential cross sections in ET jet1and  jet1 • MC area normalized to data by 0.59 • MC describes the shape of jet cross sections well 16% of the cross sections subtracted as p dissociation background (DESY-03-094) Diffractive dijets in photoproduction

  14. Differential cross sections in y and xIP y :electron energy transfer xIP: proton longitudinal momentum transfer  MC describes the shapes of data well Diffractive dijets in photoproduction

  15. Differential cross sections in MX • MX : invariant mass • of system X • Once again, shapes agree Diffractive dijets in photoproduction

  16. Differential cross section in zIPobs • zIPobs: sensitive to the parton distribution of the diffractive exchange (Pomeron) • Data is higher at high zIPobs Diffractive dijets in photoproduction

  17. Differential cross section in xobs resolved enriched direct enriched • Data/MC = 0.59 (flat) • No evidence of a resolved suppression with respect to direct at LO  ? Diffractive dijets in photoproduction

  18. Summary • Single differential cross sections of diffractive dijets in photoproduction measured using ZEUS 9900 data.Adds to the previous ZEUS analysis of 94 data with very high statistics. • Results are fairly consistent with RAPGAP (v3.00/00 H1-fit2) scaled down by 0.59 • Shape of xobs well reproduced  No evidence of a suppression of resolved with respect to direct at LO Diffractive dijets in photoproduction

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