Diffractive parton distributions and the saturation model.pdf
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DIFFRACTIVE PARTON DISTRIBUTIONS AND THE
SATURATION MODEL
K. GOLEC–BIERNAT
II Institute of Theoretical Physics, Hamburg University,
Luruper Chaussee 149, D-22761 Hamburg, Germany
and
Institute of Nuclear Physics, Radzikowskiego 152,
31-342 Krako?w, Poland
M. WU?STHOFF
Department of Physics, University of Durham,
Durham DH1 3LE, United Kingdom
We construct diffractive parton distributions in the model of DIS diffraction in
which the diffractive state is formed by the qq? and qq?g components. The interaction
of such systems with the proton is described by the dipole cross section given by
the saturation model. We find Regge factorization property with the measured at
HERA depenedence on energy. The found parton distributions are evolved with
the DGLAP evolution equations to make a comparison with the data.
1 Introduction
Collinear factorization proved for diffractive DIS 1 allows to define diffractive
quark and gluon distributions through the relation to the diffractive structure
function, e.g. in the leading log(Q2) approximation
F
D(3)
2 = 2
∑
q
e2q β q
D(β,Q2, xIP ), (1)
where qD = q?D. This relation concerns only the leading twist description. The
diffractive parton distributions (DPD) obey the DGALP evolution equations.
In the Ingelman-Schlein approach to DIS diffraction Regge factorization is
additionally assumed
qD(β,Q2, xIP ) = f(xIP ) fq(β,Q
2), (2)
where f(xIP ) is related to the soft pomeron flux
2,3. In an alternative ap-
proach, the detailed description of diffractive processes is achieved by mod-
elling the diffractive final state as well as its interaction with the proton start-
ing from perturbative QCD 4. Such an analysis goes beyond the leading twist
description and Regge factorization for the DPD is not assumed. The problem
which is faced in this approach is the strong sensitivity to nonperturbative
1
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Figure 1. The diffractive qq? and qq?g contributi
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