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Factorization Breaking in Diffractive Photoproduction of Dijets. Gustav Kramer University of Hamburg 15 april 20 04. Motivation Diffractive parton densities Multipomeron exchanges Direct and resolved photoproduction Conclusions. Motivation. Hard diffraction:

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factorization breaking in diffractive photoproduction of dijets

Factorization Breaking in Diffractive Photoproduction of Dijets

Gustav Kramer

University of Hamburg

15 april 2004

Motivation

Diffractive parton densities

Multipomeron exchanges

Direct and resolved photoproduction

Conclusions

motivation
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.

G. Kramer – Univ. Hamburg

kinematics
Kinematics

Diffractive processes at HERA:

Inclusive deep inelastic scattering:

Diffractive deep inelastic scattering:

Experimental cuts:

H1 Coll., ICHEP 02 and EPS 03.

G. Kramer – Univ. Hamburg

diffractive parton distributions
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.

G. Kramer – Univ. Hamburg

proof of hard qcd factorization
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.

G. Kramer – Univ. Hamburg

multi pomeron exchanges
Multi-Pomeron Exchanges

Direct photoproduction:

Resolved photoproduction:

 Modification of the Regge trajectory

 Factorization breaking

G. Kramer – Univ. Hamburg

diffractive photoproduction of dijets
DiffractivePhotoproductionofDijets

Cross section:

  • Photon flux: Weizsäcker-Williams approximation

G. Kramer – Univ. Hamburg

factorizable multi pomeron exchanges
FactorizableMulti-Pomeron Exchanges

y-dependence: Photon flux

xIP-dependence: Pomeron flux

 Small correlations due to exp. cuts

 Subleading Reggeon contribution

G. Kramer – Univ. Hamburg

two channel eikonal model
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.

G. Kramer – Univ. Hamburg

non factorizable multi pomeron exchanges
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

G. Kramer – Univ. Hamburg

diffractive inclusive production
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.

G. Kramer – Univ. Hamburg

factorization scale dependence
Inclusive photoproduction:

Diffractive photoproduction:

Factorization Scale Dependence

CTEQ5M1

CTEQ6L

MK, Rev. Mod. Phys. 74 (2002) 1221.

MK, G. Kramer, hep-ph/0401202.

G. Kramer – Univ. Hamburg

conclusions
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!)

G. Kramer – Univ. Hamburg

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