Marta Ruspa

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ZEUS results on inclusive diffraction

• Marta Ruspa
• Torino University
• XXXIII International Symposium
• on
• Multiparticle Dynamics
• Krakow, Poland
• September 5-11, 2003
• on behalf of

• Diffractive cross section
• Q2 and W dependences
• Diffractive structure function
• Q2 and ß dependences

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Inclusive diffraction ?p ? Xp
Exchange of color singlet producing a GAP in the
particle flow
e
p
? No activity in the forward direction ? Proton
almost intact after the collision
e(k)
Q2

• diffractive ?p cross section

e (k)
?(q)
X
?
W

• diffractive structure function
• (assumes )

IP
xIP
P (p)
P(p)
t
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Data samples

• 99-00 FPC sample
• (Mx method)
• 22 lt Q2 lt 80 GeV2
• 37 lt W lt 245 GeV
• Mx lt 35 GeV
• Higher ß region

• 97 LPS sample
• 0.03 lt Q2 lt 100 GeV2
• 25 lt W lt 280 GeV
• 1.5 lt Mx lt 70 GeV
• xL gt 0.9
• Higher xIP region

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Selection of events ?p ? Xp with Mx method

• Properties of Mx distribution
• - exponentially falling for decreasing Mx for
  non-diffractive events
• - flat vs ln Mx2for diffractive events

Diffr.
Non-diffr.
Non-diffr.
Diffr.

• Forward Plug Calorimeter (FPC)
• CAL acceptance extended by 1 unit in
  pseudorapidity from ?4 to ?5
• higher Mx and lower W
• if MN gt 2.3 GeV deposits EFPC gt 1 GeV
  recognized and rejected!

• D, c, b from a fit to data
• contamination from reaction ep?eXN

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Selection of events ?p ? Xp with LPS

• Free of p-diss background
• Low acceptance
• ? low statistics

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Data samples

• 99-00 FPC sample
• (Mx method)
• 22 lt Q2 lt 80 GeV2
• 37 lt W lt 245 GeV
• Mx lt 35 GeV
• Higher ß region

• 97 LPS sample
• 0.03 lt Q2 lt 100 GeV2
• 25 lt W lt 280 GeV
• 1.5 lt Mx lt 70 GeV
• xL gt 0.9
• Higher xIP region

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Cross section Q2 dependence
(LPS)

• Transition to a constant
• cross section as Q2?0
• (similar to total cross section )

• Main features of the
• data described by
• BEKW parametrization (xIPlt0.01)

(Bartels, Ellis, Kowalski and Wüsthoff)
medium ß
small ß

• qqg fluctuations dominant
• at low Q2

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Cross section W dependence
(Mx method)
p-dissociation events with MNlt2.3 GeV included

• MXlt 2 GeV weak W dep.
• MXgt 2 GeV d?/dMX rises
• rapidly with W

? power-like fit
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aIP from diffractive and total ?p scattering
(Mx method)
fit to diffractive cross section data

• ?IPdiff higher than soft Pomeron

• Evidence of a rise of ?IPdiff with Q2.

fit to total cross section data

• Same W dep. of diffractive and total cross
  section

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F2D(3) Q2 dependence
(LPS)

• Positive scaling violation
• at all values of xIP

• at low Q2

• Data well described by
• BGK saturation model
• (xIPlt0.01)

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F2D(3) ß dependence
(LPS)

• Different ß dep. at
• low and high xIP

• Data well described by
• BGK saturation model
• (xIPlt0.01)

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F2D(3) at fixed xIP
(Mx method)

• Maximum near ß0.5 consistent
• with a ß(1- ß) behaviour suggesting
• main contribution from a
• quark-antiquark state

• For high ß F2D(2) decrease with
• rising Q2

• As ß ? 0 F2D(2) rises. The rise
• becomes stronger as Q2 increases

Evidence for pQCD evolution
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Summary

• Recent data from ZEUS with improved precision
  and extended kinematic range
• Data described by dipole models (BEKW,
  saturation)
• W dep. of diffractive and total cross section
  similar at high Q2
• Indication that aIP increases with Q2 in
  diffraction
• F2D(3) scaling violations at all xIP
• Different ß dependences of F2D(3) in at low and
  high xIP
• F2D(2) pQCD-like evolution with ß and Q2