A QCD analysis of diffractive DIS

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A QCD analysis of diffractive DIS
and its effect on global DIS analyses
Alan Martin, Misha Ryskin and Graeme Watt

• Diffractive DIS occurs at about 10-20 the rate
  of DIS
• How should we analyse DDIS data?
• How do we treat DDIS events in global analyses of
  DIS data?

• are they in the input distributions?
• or, do we allow for them in the DGLAP evolution?

Workshop on Low x Physics Prague September
2004
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higher twist
ln Q2
Bartels,Ellis, Kowalski Wusthoff base
parametrization on these forms
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Fit to ZEUS and H1 diffractive DIS (prelim.) data
xg x -l
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Pomeron made of two gluons
Pomeron made of two sea quarks
Now Pomeron flux factors depend on Sp as well
as gp
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gD
SD
H1 have steeper Q2 dep. of S, and hence larger
g. Also no twist-4 FL
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S2 0.3 to 0.1 small, large size
val sea,g
H1
MRW
HERA
g
Survival factors calc. from 2-ch eikonal model
based on multi-Pom. exchange s channel
unitarity KKMR
S2 1
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What is the impact of the diffractive DIS
analysis on the global parton analyses to DIS and
related data? We are ready to answer the
question are the DDIS data included in the
DIS input ? or should they be allowed for in
DIS DGLAP evol ? Moreover---the diffractive
fit allows an estimate of the absorptive
corrections in global DIS fit
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Contribution of diffractive F2 to inclusive F2
Apply the AGK cutting rules to
contrib.
AGK in QCD Bartels Ryskin
Im Tel stot
DF2abs - F2D
negative (Glauber shadowing)
In pQCD, is a cut, not a pole
Lipatov has a continuous no. of compts of
different size, r1/m For each compt., DGLAP
evol. of F2D(b,Q2,m2) starts

from m ? Q
provided it is large enough
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(for x lt 0.01)
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MRST-type parametrization
Input MRST2001
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increase of gluon and sea due to absorptive
corrections
gluon
sea quarks
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Good news absorp. corr. remove need for ve
gluon But still have valence-like gluon
Pomeron-like sea quarks to
hadrons Regge xg, xS x l with lg
lS Suppose we impose lg lS, very
poor fit can get acceptable fit, but only if we
shift scale in F2(x,Q2)
from Q2 to Q2 1 GeV2
(mimicks power
corrections)
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Need Q2 ? Q21 mimicks power corr.
xg, xS ? const
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Conclusions
Diffractive DIS
New pQCD description integral over Pomeron
size, 1/m Good description of combined (prelim.)
H1, ZEUS diffractive data Need two-quark Pomeron,
in addition to two-gluon Pomeron The input forms
of the Pomeron PDFs given by QCD
diagrams Pomerons PDFs different to previous
determinations
DIS diffractive DIS

• The above F2D analysis allows an estimate of the
  absorptive corr. to F2
• removes the need for a negative gluon
• Good simultaneous fit to DDIS DIS data
• But
• gluon is still valence-like, sea Pomeron-like
• either non-pert. Pomeron does not couple to
  gluons
• or DGLAP frozen at low scales
  (power corrections)

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• Diffractive DIS occurs at about 10-20 the rate
  of DIS
• How should we analyse DDIS data?
• Use pQCD for x , b, as
  well as Q2, dep.
• Integrate over the size of
  the QCD Pomeron, 1/m
• How do we treat DDIS events in global analyses of
  DIS data?

• are they in the input distributions?
• yes, partly
  mltQ0
• or, do we allow for them in the DGLAP
  evolution?
• yes, partly
  mgtQ0