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Factorization Breaking in Diffractive Photoproduction of Dijets

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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

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

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

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

Diffractive deep inelastic scattering:

Light-cone coordinates:

- qm = (q+, q-, qT)

- Leading regions:
- H:qmO(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

Direct photoproduction:

Resolved photoproduction:

Modification of the Regge trajectory

Factorization breaking

G. Kramer – Univ. Hamburg

Cross section:

- Photon flux: Weizsäcker-Williams approximation

G. Kramer – Univ. Hamburg

y-dependence: Photon flux

xIP-dependence: Pomeron flux

Small correlations due to exp. cuts

Subleading Reggeon contribution

G. Kramer – Univ. Hamburg

Hadronic collisions:

Photoproduction:

- 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

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

R = fg/IP fIP/p / fg/p with M12 = xg zIPxIPW:

R = sdiffr. / sincl. with full kinematics:

CTEQ5M1

CTEQ6L

A. Kaidalov et al., PLB 567 (2003) 61.

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

G. Kramer – Univ. Hamburg

Inclusive photoproduction:

Diffractive photoproduction:

CTEQ5M1

CTEQ6L

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

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

G. Kramer – Univ. Hamburg

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