Inclusive Diffraction at HERA Marcella Capua INFN and Calabria University

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Inclusive Diffraction at HERAMarcella Capua
INFN and Calabria University

• experimental methods and diffractive gp cross
  section
• Regge phenomenology
• measurement of t and xIP dependence
• comparison with inclusive ep cross section
• QCD analysis of diffraction
• - diffractive pdf

• Small X and Diffraction
• FNAL Chicago (USA) 17 20 September 2003

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Diffractive ?p interactions at HERA
Q2

• large kinematic range and cross section
• the order 10 of DIS is diffractive
• 4p acceptance (important for g dissociative
  system)
• point-like couplings to probe the Pomeron
  structure
• wide Q2 range to access the transition region
  from soft
• to hard processes

W
MY
3

• Large Rapidiy Gap method
• X system and e measured
• System Y not measured, some theoretical and
  experimental uncertanties
• Integrate over tlt1GeV2 and MYlt1.6 GeV
• High acceptance

• MX method
• High acceptance
• t measurement not possible
• systematics from p-diss

• p tag method
• Measurement of t
• Free of p-diss background
• Lower acceptance

NB if scattered proton not detected, background
from proton dissociative events
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Factorization

• QCD Hard Scattering factorization (by Collins
  Trentadue, Veneziano Berera, Soper)

At fixed xIP and t diffractive Parton Densities
evolve according to DGLAP

• Regge factorization - resolved IP model (IP
  with partonic structure)

(Breit frame)
Regge motivated pomeron flux
Shape of diffractive pdfs independent of xIP and
t
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What we know about t-distribution (pTag method)
Exponential fit to t distribution
Regge phenomenology predicts shrinkage of the
diffractive peak (b rise as xIP ? 0)
For xIP lt 10 2, data prevent any firm conclusion
We are waiting new data from H1 and ZEUS proton
tagger
no Q2 dependence
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Cross section energy dependence (MX method)
Fit
As expected for soft IP

• MX lt 2 GeV (resonance range) weak W
  dependance
• MX gt 2 GeV d?/dMX rises with Q2 adiff
  typically higher then soft

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Energy dependence (MX method)
diffractive cross section
total cross section
Data (4ltMXlt8 GeV) consistent with the same
W-dependence for the diffractive and the total
cross section
value of ?IP diff higher than soft
Pomeron indication of a rise of ?IPdiff with Q2.
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Ratio ?diff/?tot (MX method)
Regge th

• low MX strong decrease of ?diff/?tot
• with increasing Q2
• high MX no Q2 dependence

?diff(MXlt35 GeV)/?tot 20 Q2 2.7 GeV ? 10
Q2 27 GeV

• at W220 GeV

In DIS ?diff/?tot independent of W !
Same results from H1 and ZEUS-LPS
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H1 Measurement of srD(3) (LRG method)
New low and very high Q2 data!!! Agreement
between measurements Red sample used for DGLAP
QCD interpretation and aIP(0) calculation well
described by the fit
FL unknown, FL 0 or FL F2 ? few error
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b and Q2 dependences
large scaling violation except at high b ? gluon
dominated similar at all xIP ? support for Regge
factorization
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NLO DGLAP QCD fit
-Regge factorization -Singlet S and gluon g with
Q203GeV2 -NLO DGLAP evolution -Fit medium Q2 (6
lt Q2 lt 120 GeV2) -Experimental and theor
incertainties
Diff PDFs Extended to large z Gluon dominate S
well constrained
Gluon momentum fraction 75 15 at Q2 10
GeV2 and remains large up to high Q2
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Test of QCD factorization
Good agreement with prediction with NLO fit at
medium Q2
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Summary

• recent data from H1 and ZEUS with improved
  precision and extended
• kinematic range
• data prevent any firm conclusion about shrinkage
  (waiting for new proton
• tagged data)
• value of diffractive ?IP higher than soft
  Pomeron
• W-dependence of diffractive and total cross
  section similar on DIS
• similar Q2 and b dependencies to the inclusive
  DIS at medium b
• NLO QCD fit of inclusive diffractive gives a
  good description of the data
• diffractive pdf dominated by gluons
• diffractive pdf predictions well confirmed by
  tests