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Inclusive Diffraction at HERA From The ZEUS
Experiment
Presented by B.Loehr on behalf of ZEUS
New data from the running period 1999-2000.
The last period with the ZEUS Forward Plug
Calorimeter (FPC) and the Leading Proton
Spectrometer (LPS) installed.
Results from all three methods to extract
inclusive diffractive events

• Leading proton spectrometer
• The MX method
• Large rapidity gap method

using data from the same running period.
We attempt to get a consistent picture from these
three method.
Bernd Löhr, DESY
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Diffraction 2006 , 5-10 September , Milos Greece
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Extraction of diffractive events (I)
1.) Forward proton detection
-gt diffractively scattered proton
the only method to measure the t-distribution
Forward proton tagged events are practically
free of proton dissociation background.
ZEUS preliminary
0.4 0.6 0.8 1.0
They contain, however, contributions from Reggeon
exchange at high xIP or low xL.
xL
LPS has small acceptance
2.) The large (pseudo)rapidity (?max) method
No tracks or energy deposits in calorimeter for
rapidities greater than ?max or at angles less
than ?min.
Events tagged by a large rapidity are
dominated by diffraction but they contain
contributions from proton dissociation and from
Reggeon exchange.
Bernd Löhr, DESY
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Diffraction 2006 , 5-10 September , Milos Greece
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Extraction of diffractive events (II)
3.) The Mx-method
(ii) Diffractive events
(i) Nondiffractive events
Uncorrelated particle emission between incoming
p-direction and scattered quark.
At high energies and not too low MX
Rapidity
Property of a produced particle
(iii) Nondiffractive diffractive contributions
W
Poisson distr. for Dy in nondiffractive events
For
Fit slope b and c -gt subtract nondiffractive
events.
Bernd Löhr, DESY
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The ZEUS MX-Analysis (I)
Example of lnMX-distributions for four
kinematical bins
Diffractive data selected by the MX-method
contain proton dissociative events but no
contributions from Regge exchange
MC-simulation
nondiffractive DJANGOH diffractive
SATRAP proton diss. SANG
SANG adjusted to fit data which are dominated by
proton dissociation
Proton dissociation can be reliably calculated
for MN gt 2.3 GeV and has been subtracted from
data
The ZEUS MX-results contain contributions
from proton dissociation for masses MN lt 2.3 GeV.
fit to data in the fit region
fitted slope of of nondiffractive events
Data are presented for 9 Q2-bins, 7 W-bins, and 6
MX-bins at reference values Q2ref, Wref, MXref
Bernd Löhr, DESY
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ZEUS MX data from 1998 2000 (II)
Mx 98-99, Mx 99-00 (prel.)

Mx 98-99

Published data from 1998-1999 period
(ZEUS Coll., S.Chekanov et al. Nucl. Phys B 713,
3 (2005) )

Prel. Mx 99-00
Preliminary results from 1999-2000
period. Extension of Mx 98-99 analysis to higher
Q2.
Mx 98-99 and Mx 99-00 analyses have common bin
at Q2 25 GeV2
Bernd Löhr, DESY
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ZEUS Mx 98-99, ZEUS Mx 00 (prel.)
ZEUS MX data from 1998 2000 (III)

Mx 98-99

Prel. Mx 99-00

Mx 98-99 and Mx 99-00 analyses have common bin
at Q2 55 GeV2
Within syst. errors good agreement between Mx
98-99 and Mx 99-00 results
Bernd Löhr, DESY
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Fit W-dependence of inclusive DIS and inclusive
diffractive DIS cross sections
Inclusive DIS
For small x, F2 rises rapidly as x-gt 0
lt
lt
lt
Inclusive diffractive DIS
averaged over t
for small t.
Inclusive DIS and inclusive diffractive DIS are
not described by the same Pomeron.
take
as measure by ZEUS LPS
Bernd Löhr, DESY
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Ratio of total diffractive cross-section to total
DIS cross-section
Ratio plotted at W220 GeV because only there
the full MX range is covered by measurments
r sdiff(0.28ltMXlt35 GeV)/stot at W220 GeV
Within the errors of the measurements r is
independent of W.
Mx 98-99
Mx 99-00 (prel.)
At W220 GeV, r can be fitted by
r 0.22 0.034.ln(1Q2)
This logarithmic dependence of the ratio of total
diffractive cross-section to the total DIS cross
section indicates that diffraction is a leading
twist process for not too low Q2.
Bernd Löhr, DESY
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Diffractive Cross-Section and Diffractive
Structure Functions
If t is not measured (LRG and MX-method )
H1 defines
sizable only at high y
ZEUS neglects the contribution from longitudinal
structure function
If is interpreted in
terms of quark densities, it specifies the
probability to find in a proton which undergoes a
diffractive interaction a quark carrying a
fraction x bxIP of the proton momentum.
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Bernd Löhr, DESY
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xIPF2D(3) Results from the MxII-Analysis
ZEUS Mx 99-00 (prel.)
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Bernd Löhr, DESY
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ZEUS modified BEKW Fit
The ZEUS data support taking nT(Q2) ng(Q2)
n1ln(1Q2/Q20) and nL 0
Taking x0 0.01 and Q20 0.4 GeV2 results in
the modified BEKW model (BEKW(mod)) with the 5
free papameters
cT , cL , cg , n1T,g , g
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Bernd Löhr, DESY
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xIPF2D(3) Results from the MxI and MxII-Analyses
with BEKW(mod) Fit (I)
BEKW-fit (prel.)
transverse qq contribution
sum of all contributions
gt 400 points, 5 parameters c2/nD 0.71 , total
errors
transverse qqg contribution
longitudinal qq contribution
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Bernd Löhr, DESY
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xIPF2D(3) Results from the FPC I II MX-Analyses
with BEKW(mod) Fit II
Result of the BEKW(mod) fit
xIPF2D(3) shows considerable scaling
violations from positive scaling violations
over near constancy to negative scaling
violations.
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Bernd Löhr, DESY
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xIPF2D(3) Results from the FPC I II MX-Analyses
with BEKW(mod) Fit ( III)
ZEUS Mx 99-00 (prel.)

• xIPF2D(3) exhibits
• a broad maximum around b0.5
• which is due to the transverse
• qq-contribution,
• a steep rise towards small b
• which is generated by the
• qqg-contribution,
• a longitudinal qqg-contribution
• which is sizeable only at
• very high b and causes the structure
  function not to
• vanish at b 1.

-
-
-
-
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Diffraction 2006 , 5-10 September , Milos Greece
Bernd Löhr, DESY
Bernd Löhr, DESY
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xIPF2D(3) Results from the FPC I II MX-Analyses
with BEKW(mod) Fit (IV)
ZEUS Mx 99-00 (prel.)
Fixed xIP 0.01
25 lt Q2 lt 190 GeV2 in one plot
The 3 contributions from BEKW(mod) fit for the
above Q2 values plotted
-
-
longitudinal qq-contributions
qqg-contributions
The BEKW model has an effective QCD-type
Q2-evolution incorporated.
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Bernd Löhr, DESY
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ZEUS Results from the LPS I
Diffractive structure functions from ZEUS LPS
mesurements
Regge fit
t 0.13 GeV2
t 0.3 GeV2
ZEUS LPS 00 (prel.)
ZEUS LPS 00 (prel.)
Fit parameters
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Bernd Löhr, DESY
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ZEUS Results from the LPS (II)
Comparison of LPS results with recent H1 FPS
results
ZEUS LPS 00 (prel.), H1 FPS 06
RD 0 -gt
Not shown are the normalization Uncertainties of
12/-10 for the ZEUS LPS data and /-10 for
the H1 FPS data.
The agreement is good
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Bernd Löhr, DESY
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ZEUS Results from the LRG Method (I)
Events selected by hmax lt 3.0 and energy in
the Forward Plug Calorimeter (FPC) lt 1 GeV
ZEUS LRG 00 (prel.)
ZEUS LRG 00 (prel.)
Results of a Regge-fit
Input parameters to the Regge -fit aIR(0)
0.75, BIR 2.0 GeV-2 aIP 0.0 GeV-2 , BIP
7.2 GeV-2
Fit results aIP(0) 1.117 /-0.005 0.024
-0.007
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Bernd Löhr, DESY
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ZEUS Results from the LRG Method (II)
Comparison of ZEUS LRG data with LPS data
ZEUS LRG 00 (prel.)
ZEUS LRG 00 (prel.), ZEUS LPS 00 (prel.)
The ratio LPS/LRG 0.82 /- 0.01(stat.) /-
0.03(syst) it is independent of Q2 and b
The Regge-fit gives a good description of the
ZEUS LRG data with c2/ndf 159/185
Not shown is the normalization uncertainty of
the LPS measurement of about 10.
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Bernd Löhr, DESY
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ZEUS Comparison of Results from the MX-, and
LRG- Method (I)
ZEUS MX 98-99, ZEUS MX 99-00 (prel.), ZEUS LRG
00 (prel.)
In general good agreement for xIP lt 0.01
For xIP gt 0.01 one can expect some differences
from Reggeon contributions to the LRGdata.
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Bernd Löhr, DESY
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ZEUS Comparison of Results from the MX-, and
LRG- Method (II)
ZEUS MX 99-00, ZEUS MX 99-00 (prel.), ZEUS LRG 00
(prel.)
Comparison of ZEUS LRG with ZEUS MX results
xIPF2D(3) as a function of Q2
ZEUS Mx 90-99
ZEUS Mx 99-00 (prel.)
ZEUS LRG 00 (prel.)
Reasonable agreement, maybe there is a
normalization difference.
Work is continuing to understand remaining
differences
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Bernd Löhr, DESY
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Summary

• ZEUS presented preliminary results on inclusive
  diffraction from
• 3 different methods for the extraction of
  inclusive diffractive events.
• Results from all 3 methods are derived from
  data taken during the same time.
• The results span a wide range of the kinematic
  region up to high Q2.
• There is good to reasonable agreement for the
  results from all 3 methods.
• In particular, there is agreement for the
  Q2-dependence of the structure function
• between the MX-method and the LRG-method.
• There is also good agreement compared to
  results from H1 for the
• LRG- and FPS method.
• Work continues to understand some remaining
  minor differences, in particular
• with respect to the relative normalisations.
• We try to get a consistent picture out of the
  results from these three methods.

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Bernd Löhr, DESY