Odderon Searches

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Vth Workshop on Small-x and Diffractive Physics
Odderon Searches and Hadronic Final
States in Diffractive Scattering at
HERA Karlheinz Meier Kirchhoff-Institut für
Physik Ruprecht-Karls-Universität Heidelberg
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Language of Diffraction in a factorized view
Q2 (momentum transfer describing photon virtuality
Mi (inclusive final state mass)
Mx (exclusive final state mass)
z momentum fraction wrt. pomeron
W (?p mass)
x momentum fraction wrt. proton, only energy,
momentum, angular momentum transferred here
M mp (proton or excited and decaying nucleon
resonance)
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Language of Diffraction in a factorized view
Q2 (momentum transfer describing photon virtuality
Mi (inclusive final state mass)
Mx (exclusive final state mass)
z momentum fraction wrt. pomeron
W (?p mass)
x momentum fraction wrt. proton, only energy,
momentum, angular momentum transferred here
?
M mp (proton or excited and decaying nucleon
resonance)
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H1 Excl. Meson Production via C 1 and C -1
Exchange
1 photon ? C -1
2 gluons ? C 1
3 gluons ? C -1
Idea Unambiguous measurement of final state
charge conjugation C look into pure photonic
decays, count photons ODD number photons means
POMERON exchange EVEN number of photons means
ODDERON exchange
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The Stochastic Vacuum Model (SVM) of Dosch and
Simonov
Quantitative prediction for exclusive meson
production via Odderon exchange based on a
non-perturbative QCD approach exists Stochastic
Vacuum Model (SVM) Dosch and Simonov, Phys.Lett.
B205 (1988) Nachtmann, Ann.Phys. 209 (1991) Dosch
Phys.Rev. D50 (1994) Berger, Donnachie, Dosch,
Kilian, Nachtmann, Rüter, Eur. Phys. J. C9
(1999) Berger et al. Eur.Phys. J. C14
(2000) Model has successfully described a
variety of high energy reactions (e.g. J/?
Production at HERA) Donnachie, Dosch, Phys. Rev.,
D65 (2002) The H1 approach of photon counting is
a clean test of this non-perturbative QCD
approach based of purely electromagnetic probes
with small experimental ambiguity Problem No
prediction of energy dependence, SVM calculations
carried out for W 20 GeV, Regge-Theory used for
extrapolation, Odderon Intercept ??
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H1 Expected Signals, Backgrounds and Topologies
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H1 Excl. ?? ? 2? Production (C -1 Exchange,
Odderon)
Ensure exclusive final states via longitudinal
momentum balance Explicit detection of neutron in
upstream 0-degree calorimeter L 30.6
pb-1 important cross-check inclusive ?? is
clearly seen at correct rate
no signal observed, limit at 95 C.L. ?(?p) ? ??
N ? ?? N lt 49 nb expectation from SVM is
200 nb
Search for Odderon-Induced Contributions to
Exclusive ?? Photoproduction at HERA H1
Collaboration, C. Adloff et al., Phys. Lett.
B544
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H1 Excl. ?? ? 3? Production (C 1 Exchange,
Pomeron)
Ensure exclusive final states via longitudinal
momentum balance L 4.95 nb-1 clear intermediate
?? signal seen and used for event selection
clear signal observed ?(?p) ? ?? X ? ??? X
1250 ?180 (sta.) ? 220 (sys.) nb well in line
with Regge fits (e.g. Cudell et al. Phys.Rev. D61
(2000).
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H1 Excl. f2 ? 4? Production (C -1 Exchange,
Odderon)
Ensure exclusive final states via longitudinal
momentum balance L 4.95 nb-1 ?? mass windows
used for event selection
no clear signal observed, limit at 95
C.L. ?(?p) ? f2 X ? ???? X lt 16
nb expectation from SVM is 21 nb
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H1 Excl. a2 ? 4? Production (C -1 Exchange,
Odderon)
Ensure exclusive final states via longitudinal
momentum balance L 4.95 nb-1 ?? and ? mass
windows used for event selection
no signal observed, limit at 95 C.L. ?(?p) ? a2
X ? ???? X lt 96 nb expectation from SVM is
190 nb
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H1 Excl. ????(b1) ? 5? Production (C 1
Exchange, Pomeron)
Ensure exclusive final states via longitudinal
momentum balance L 4.95 pb-1 ?? and ?? mass
windows used for event selection
clear signal observed ?(?p) ? ?? ?? X ? ?????
X 980 ? 200 (stat.) ? 200 (sys.)
nb compatible with dominant resonant part from b1
? ?? ?? (1- - pseudovector) expect 190 nb from
non-resonant PYTHIA generator, 660 nb from Regge
fit to low energy data (Omega-Photon
Collaboration Nucl.Phys. B243 (1984))
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Summary H1 Analysis of Exclusive Multiphoton
Final States
Clear Picture A very clean test of a
non-perturbative QCD prediction (SVM) has been
performed. Only exclusive final states with odd
number of photons are observed and in good
agreement with expectations from Pomeron
exchange. Even number states can be detected but
are not seen. Limits clearly exclude the
predictions from the SVM model (Dosch,
Berger) The Odderon has not been seen
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Language of Diffraction in a factorized view
Q2 (momentum transfer describing photon virtuality
Mi (inclusive final state mass)
Mx (exclusive final state mass)
z momentum fraction wrt. pomeron
W (?p mass)
x momentum fraction wrt. proton, only energy,
momentum, angular momentum transferred here
M mp (proton or excited and decaying nucleon
resonance)
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H1 LO and NLO Fits of Diffractive Parton
Distributions
LO and NLO QCD fits to inclusive diffractive DIS
data Contributions from light flavour singlet and
gluons ( reggeon contribution for high
xP) Evolution based on DGLAP equations Theoretical
uncertainties from ?QCD and charm-quark
mass Gluon dominance
Use for calculation of various diffractive cross
sections (2-Jets, charmed mesons)
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Language of Diffraction in a factorized view
Q2 (momentum transfer describing photon virtuality
Mi (inclusive final state mass)
Mx (exclusive final state mass)
z momentum fraction wrt. pomeron
W (?p mass)
x momentum fraction wrt. proton, only energy,
momentum, angular momentum transferred here
M mp (proton or excited and decaying nucleon
resonance)
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H1 Diffractive 2-Jet Production in Deep
Inelastic Scattering
Data from H1 Eur.Phys.J. C20
(2001) 4 lt Q2 lt 80 GeV2 Use both, NLO (?s2) QCD
matrix elements for parton scattering (DISENT
implementation) and NLO diffractive parton
distributions in addition to Regge-factorisation
for the Pomeron DISENT NLO set-up µT2 pT2
(varied for systematics) µf2 40 GeV2 ?4QCD
200 MeV Hadronisation corrections
LO (without parton shower) far below data, better
description with full NLO including errors from
renormalization scale (20) but not from
diffractive parton distributions
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H1 Other 2-Jet DIS distributions compared to
full NLO
Consistent picture Decrease of NLO corrections
for larger Q2 NLO describes all distributions in
shape and normalisation reasonable well
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H1 Diffractive 2-Jet Production with Real
Photons (Q2 0)
Jets pT,1(2) gt 5(4) GeV Compare to leading
order matrix element Monte-Carlo with parton
showers taking care of higher order effects
RAPGAP Use new LO fit for diffractive parton
distributions from H1 and compare to previous
fit.
New LO fit with LO Monte-Carlo including parton
shower describes data well, major improvement
compared to old fit.
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H1 Diffractive 2-Jets (Q2 0) for different x?
x? 1 Direct, DIS like Interaction x? lt 1
Resolved, Hadron-Hadron like Interaction
Continuous (all x?) good description of H1
photoproduction 2-Jet data with model based on
new LO Fit Fit equally well suited for DIS and
photoproduction, no indication of factorisation
failure
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H1 Diffractive D? Production in Deep Inelastic
Scattering
Data from H1 Phys.Lett. B520
(2001) 2 lt Q2 lt 100 GeV2 Use both, NLO
calculation for D (HVQDIS) and NLO diffractive
parton distributions in addition to
Regge-factorisation for the Pomeron HVQDIS NLO
set-up µT2 Q2 4mc2 (mc 1.5 GeV) (varied
for systematics) µf2 µT2 ?4QCD 200
MeV Peterson fragmentation function
Good agreement between full NLO calculation and
data in shape and normalisation, NLO correction
smaller than for jet production
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H1 Other D DIS distributions compared to full
NLO
Consistent picture Some decrease of NLO
corrections for larger Q2 NLO describes all
distributions in shape and normalisation
reasonable well
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ZEUS Diffractive D? Production in Deep
Inelastic Scattering
DESY-03-094 1.5 lt Q2 lt 200 GeV2 0.02 lt y lt
0.7 XP lt 0.035 ? lt 0.8 pT(D) gt 1.5 GeV ?(D) lt
1.5 Signal of 4976 ?103 Mesons (cross section
0.521 nb)
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ZEUS Diffractive Event Fraction for Open Charm
Diffractive fraction of of open charm is 6.4 No
strong dependence on W, Q2, x(D) Rather distinct
dependence on pT and ?, well understood in the
framework on NLO QCD
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ZEUS Differential Open Charm Cross-Section
NLO calculation with (old) gluon dominated fit to
diffractive parton distribution functions
(ACTW-B) gives good description of data Two gluon
echange models SATRAP and BJLW. BJLW with gluon
pT cut describes data only for low xP
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ZEUS Extraction the Open Charm Contribution to
F2D
Compare to NLO QCD with different fits to
diffractive structure function (ACTW) Clear
preference for gluon dominated fit B, other fits
completely excluded Consistent set of diffractive
structure function found (e.g. jets and open
charm)
Rather strong dependence on gluon behaviour in
structure function
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Conclusions

• Final States from (real) Diffraction have
  reached a very detailed level of understanding
• The factorisation picture works at HERA for
  virtual as as well as for real photons
• Consistent modelling of jets and charmed meson
  production in complete NLO is in agreement with
  the data taken.
• The exchange of vacuum quantum numbers (i.e.
  the Pomeron) is sufficient to describe all HERA
  data. There is so far no experimental hint for
  the existence of the Odderon (3 gluons....?).
  However, statistics only allows to probe the
  level of the SVM prediction. There is a lot to
  gain from HERA II in this area.