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Breaking Factorization: Diffractive (Photo-)Production of Dijets

This presentation by Michael Klasen discusses the complexities of diffractive parton densities and the role of multipomeron exchanges in photoproduction, particularly focusing on dijets. Klasen explores whether factorization holds across different Q² regimes and assesses direct and resolved photoproduction mechanisms from low to high Q². Key points include the effects of next-to-leading order (NLO) calculations, experimental findings from HERA, and implications for hard diffraction phenomenology. The conclusions highlight ongoing debates about factorization and new observables in diffractive processes.

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Breaking Factorization: Diffractive (Photo-)Production of Dijets

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  1. Factorization Breaking in Diffractive (Photo-)production of Dijets Michael Klasen UJF / LPSC Grenoble 16 september 2004 Motivation Diffractive parton densities Multipomeron exchanges Direct and resolved photoproduction: From low to high Q2 Conclusions

  2. Motivation Hard diffraction:  Does factorization hold? Deep inelastic scattering: Yes.  Direct photoproduction Hadroproduction: No.  Resolved photoproduction Diffractive hadroproduction of dijets: • Why next-to-leading order? • stot =sdir(xg,Mg)+sres(xg,Mg) • AtLOxg =1,butatNLOxg 1 • log(Mg)-dependence cancels CDF Coll., PRL 84 (2000) 5043. Michael Klasen - LPSC Grenoble

  3. Kinematics Diffractive processes at HERA: Inclusive deep inelastic scattering: Diffractive deep inelastic scattering: Experimental cuts: H1 Coll., ICHEP 02 and EPS 03. Michael Klasen - LPSC Grenoble

  4. Diffractive Parton Distributions Double factorization: 1. Hard QCD factorization: 2. Regge factorization: Pomeron flux factor (integrated over t): Pomeron trajectory: Ingelman, Schlein, PLB 152 (1985) 256. Michael Klasen - LPSC Grenoble

  5. Proof of Hard QCD Factorization Diffractive deep inelastic scattering: Light-cone coordinates: • qm = (q+, q-, qT) • Leading regions: • H: qmO(Q) • J: lm  (0,Q/2,0T) • A: |km|« O(Q) • Soft gluon attachments: • Poles in k+-plane: • Finalstate: Upper half-plane • Initial state: Lower half-plane J.C. Collins, PRD 57 (1998) 3051. Michael Klasen - LPSC Grenoble

  6. Multi-Pomeron Exchanges Direct photoproduction: Resolved photoproduction:  Modification of the Regge trajectory  Factorization breaking Michael Klasen - LPSC Grenoble

  7. DiffractivePhotoproductionofDijets Cross section: • Photon flux: Weizsäcker-Williams approximation Michael Klasen - LPSC Grenoble

  8. FactorizableMulti-Pomeron Exchanges y-dependence: Photon flux xIP-dependence: Pomeron flux  Small correlations due to exp. cuts  Subleading Reggeon contribution Michael Klasen - LPSC Grenoble

  9. Hadronic collisions: Photoproduction: Two-Channel Eikonal Model • Generalized vector meson dominance: • JPC= 1--:g  r, w, … • Fitted parameters (W = 200 GeV): • Total cross section: stot(rp)=34 mb • Pomeron slope: B = 11.3 GeV-2 • Transition probability: g = 0.6 •  ZEUS Coll., EPJ C2 (1998) 247 •  H1 Coll., EPJ C13 (2000) 371 Survival probability: Opacity / optical density: Ki = 1  g • Survival probability: • R  |S|2 0.34 Kaidalov et al., EPJ C21 (2001) 521. Kaidalov et al., PLB 567 (2003) 61. Michael Klasen - LPSC Grenoble

  10. Non-FactorizableMulti-Pomeron Exchanges xg-dependence: Direct/resolved photons zIP-dependence:  In LO, R = 1 agrees better with data!  Smaller uncertainties in 1/s ds/dz Michael Klasen - LPSC Grenoble

  11. ZEUS Analysis xg-dependence: Direct/resolved photons Other observables:  In LO, R = 1 agrees better with data!  Excellent agreement for absolute s’s! Michael Klasen - LPSC Grenoble

  12. R = fg/IP  fIP/p / fg/p with M12 = xg zIPxIPW: R = sdiffr. / sincl. with full kinematics: Diffractive / Inclusive Production CTEQ5M1 CTEQ6L A. Kaidalov et al., PLB 567 (2003) 61. MK, G. Kramer, hep-ph/0401202. Michael Klasen - LPSC Grenoble

  13. Inclusive photoproduction: Diffractive photoproduction: Factorization Scale Dependence CTEQ5M1 CTEQ6L MK, Rev. Mod. Phys. 74 (2002) 1221. MK, G. Kramer, hep-ph/0401202. Michael Klasen - LPSC Grenoble

  14. Q2-dependence: zIP-dependence: High- to Low-Q2 Transition in DIS MK, G. Kramer, to appear. MK, G. Kramer, to appear. Michael Klasen - LPSC Grenoble

  15. Conclusions Hard diffraction: Factorizable or not? • Deep inelastic scattering: Yes.  Diffractive parton densities • Hadronic scattering: No.  Multipomeron exchanges • Diffractive photoproduction of dijets at NLO: • Direct / resolved photoproduction: xg and Mg dependence • (Non-) factorizable multipomeron exchanges • Two-channel eikonal model: • Generalized vector meson dominance: g  r, w, … • Rapidity gap survival probability: R = 0.34 • Related process: • Leading neutron with p-exchange (NB: fq/p, not fg/IP!) Michael Klasen - LPSC Grenoble

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