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Forward Jets and Particles in ep collisions and parton dynamics

Forward Jets and Particles in ep collisions and parton dynamics. On behalf of H1 and ZEUS Collaborations. Parton dynamics at high energies Central region Forward Jets Forward  0 Conclusions. Jacek Turnau, Institute of Nuclear Physics, Cracow. ep (27.5 + 820 GeV) collisions. DGLAP.

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Forward Jets and Particles in ep collisions and parton dynamics

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  1. Forward Jets and Particles in ep collisions and parton dynamics On behalf of H1 and ZEUS Collaborations • Parton dynamics at high energies • Central region • Forward Jets • Forward 0 • Conclusions Jacek Turnau, Institute of Nuclear Physics, Cracow ep (27.5 + 820 GeV) collisions

  2. DGLAP BFKL CCFM QCD Evolution at low x At low x scattered parton usually descends from long cascade of parton branchings.

  3. kt ordered initial state radiation RAPGAP DIR Resolved photon CCFM evolution equation RAPGAP RES at scale Q2 + pt2 (jets) or Q2 + 4pt2 (0) CASCADE 1.0 Comparison of the data to MC models with different QCD dynamics No kt ordering in initial state radiation

  4. Inclusive Jets in DIS 5< Q2 <100 GeV2, 0.2 < y <0.6 incl. kT algorithm in Breit frame DGLAP description gradually deteriorates when going from backward to forward direction • Forward region: • huge NLO correction • large deviations at small Q2 & ET Moral: NNLO may be important in forward region

  5. Forward jets : forward region under special scrutiny Large xjet/xbj to enhance phase space for BFKL evolution to suppress DGLAP evolution

  6. Forward jet (incl. kt algo.) Forward Jets (1997) • DGLAP direct : too low • CCFM: too high • DGLAP (DIR+RES): OK similar pattern of agreement/disageement for xjet, pTjet

  7. Forward jets in ZEUS detector • Forward jets are experimentally difficult: • Interference with proton remnant • Hadronic corrections strongly model dependent at small x

  8. Forward jets forward particles (0) jet 0 fragmentationby Lund model or convolution with FF algorithms There is another interesting aspect of bringing particle into the game - later

  9. Forward 0 cross section : x dependence Best description: direct + resolved at scale 2 = Q2 +4pT2 DGLAP direct: too low CCFM too low at small x Mod. LO BFKL tuned to H1 1997 data + recent FF describes the data Similar pattern of agreement/disagreement for other distributions

  10. Overview of description of jet/particle x-sections Something wrong either in mod. LO BFKL (KMO) or CASCADE

  11. Transverse energy flow associated with forward 0 • In hadronic CMS: • 0 close to proton (most forward) • 0 towards to photon (less forward)

  12. SUMMARY AND CONCLUSIONS • Forward jets at HERA: after ~10 years description still difficult. • NLO DGLAP not enough to describe forward jet data • DGLAP direct + resolved describes the fwd jet & 0 data • Energy flow pattern slightly favors DGLAP direct + resolved in comaprison with other schemes • Mod. LO BFKL tuned to jet data describes 0 data • CCFM slightly overshoots jet data and underestimates 0 data • There seems to be contradiction between last two points : something must be wrong...

  13. Forward jets and BFKL Modified LO BFKL calculation Kwiecinski, Martin Outhwaite hep-ph/9903439 H1 1997 jet data corrected to parton level with CASCADE Normalization very sensitive to infrared cut-off k0 and scale for S

  14. Modified LO BFKL calculation Kwiecinski, Martin Outhwaite hep-ph/9903439

  15. Forward Jets

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