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Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
Odderon Searchesand
Hadronic Final Statesin
Diffractive Scattering at HERA
Karlheinz MeierKirchhoff-Institut für PhysikRuprecht-Karls-Universität Heidelberg
Vth Workshop on Small-x and Diffractive Physics
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
Mx (exclusive final state mass)
Mi (inclusive final state mass)
M ≥ mp (proton or excited and decaying nucleon resonance)
W (p mass)
Language of Diffraction in a factorized view
x momentum fraction wrt. proton, only energy, momentum, angular momentum transferred here
z momentum fraction wrt. pomeron
Q2 (momentum transfer describing photon virtuality
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
Mx (exclusive final state mass)
Mi (inclusive final state mass)
M ≥ mp (proton or excited and decaying nucleon resonance)
W (p mass)
Language of Diffraction in a factorized view
x momentum fraction wrt. proton, only energy, momentum, angular momentum transferred here
z momentum fraction wrt. pomeron
Q2 (momentum transfer describing photon virtuality
?
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
H1 : Excl. Meson Production via C = +1 and C = -1 Exchange
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
„2 gluons“ C = +1
1 photon C = -1
„3 gluons“ C = -1
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
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 ??
The Stochastic Vacuum Model (SVM) of Dosch and Simonov
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
JPC Mass (MeV/c2)Γ (MeV/c2)
Predicted σp
exchange2 clusterevents
3 clusterevents
4 clusterevents
5 clusterevents
π° → BR = 1
0 − + 139.67.7 ⋅ 10-6
200 nbOdderon
SignalChannel
negligible negligible negligible
ω° → π° → BR = 0.085 ⋅ 1
1 − − 782.68.44
300 nbPomeron
negligibleSignalChannel negligible negligible
f2 → π°π° → BR = 0.282 ⋅ 1 ⋅ 1
2 + + 1275.4185.1
21 nbOdderon
negligible negligible SignalChannel
negligible
a2 → π°η → BR = 0.145 ⋅ 1 ⋅ 0.393
2 + + 1318.0107
190 nbOdderon
negligible negligibleSignalChannel
negligible
ω°π° → BR = 0.085 ⋅ 1⋅ 1
1 + − no n resonant 1200 nbPomeron
negligible Background Background SignalChannel
b1 → ω°π° → BR = 1⋅ 0.085 ⋅ 1⋅ 1
1 + − 1229.5142
600 nbPomeron
negligible Background Background SignalChannel
H1 : Expected Signals, Backgrounds and Topologies
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
Search for Odderon-Induced Contributions to Exclusive π Photoproduction at HERA
H1 Collaboration, C. Adloff et al., Phys. Lett. B544
H1 : Excl. π 2 Production (C = -1 Exchange, Odderon)
no signal observed, limit at 95% C.L.σ(p) π + N* + N* < 49 nbexpectation from SVM is 200 nb
Ensure exclusive final states via longitudinal momentum balance
Explicit detection of neutron in upstream 0-degree calorimeter
= 30.6 pb-1
important cross-check : inclusive π is clearly seen at correct rate
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
H1 : Excl. ω 3 Production (C = +1 Exchange, Pomeron)
clear signal observedσ(p) ω + X + X = 1250 180 (sta.) 220 (sys.) nbwell in line with Regge fits (e.g. Cudell et al. Phys.Rev. D61 (2000).
Ensure exclusive final states via longitudinal momentum balance
= 4.95 nb-1
clear intermediate π signal seen and used for event selection
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
H1 : Excl. f2 4 Production (C = -1 Exchange, Odderon)
no clear signal observed,limit at 95% C.L.σ(p) f2 + X + X < 16 nbexpectation from SVM is 21 nb
Ensure exclusive final states via longitudinal momentum balance
= 4.95 nb-1
π mass windows used for event selection
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
H1 : Excl. a2 4 Production (C = -1 Exchange, Odderon)
no signal observed,limit at 95% C.L.σ(p) a2 + X + X < 96 nbexpectation from SVM is 190 nb
Ensure exclusive final states via longitudinal momentum balance
= 4.95 nb-1
π and η mass windows used for event selection
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
H1 : Excl. πω(b1) 5 Production (C = +1 Exchange, Pomeron)
clear signal observedσ(p) ω + π + X + X = 980 200 (stat.) 200 (sys.) nb
compatible with dominant resonant part from b1 ω + π (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))
Ensure exclusive final states via longitudinal momentum balance
= 4.95 pb-1
π and ω mass windows used for event selection
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
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
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
Mx (exclusive final state mass)
Mi (inclusive final state mass)
M ≥ mp (proton or excited and decaying nucleon resonance)
W (p mass)
Language of Diffraction in a factorized view
x momentum fraction wrt. proton, only energy, momentum, angular momentum transferred here
z momentum fraction wrt. pomeron
Q2 (momentum transfer describing photon virtuality
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
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)
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
Mx (exclusive final state mass)
Mi (inclusive final state mass)
M ≥ mp (proton or excited and decaying nucleon resonance)
W (p mass)
Language of Diffraction in a factorized view
x momentum fraction wrt. proton, only energy, momentum, angular momentum transferred here
z momentum fraction wrt. pomeron
Q2 (momentum transfer describing photon virtuality
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
H1 : Diffractive 2-Jet Production in Deep Inelastic Scattering
Data from H1 Eur.Phys.J. C20 (2001)
4 < Q2 < 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 :µT
2 = 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
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
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
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
H1 : Diffractive 2-Jet Production with Real Photons (Q2 ≈ 0)
Jets : pT,1(2) > 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.
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
H1 : Diffractive 2-Jets (Q2 ≈ 0) for different x
x = 1 : Direct, DIS like Interaction
x < 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
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
H1 : Diffractive D* Production in Deep Inelastic Scattering
Data from H1 Phys.Lett. B520 (2001)
2 < Q2 < 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 :µT
2 = Q2 + 4mc2 (mc= 1.5 GeV)
(varied for systematics)µf
2 = 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
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
Consistent picture
Some decrease of NLO corrections for larger Q2
NLO describes all distributions in shape and normalisation reasonable well
H1 : Other D* DIS distributions compared to full NLO
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
ZEUS : Diffractive D* Production in Deep Inelastic Scattering
DESY-03-094
1.5 < Q2 < 200 GeV2
0.02 < y < 0.7
XP < 0.035
< 0.8
pT(D*) > 1.5 GeV
|η(D*)| < 1.5
Signal of 4976 103 Mesons
(cross section 0.521 nb)
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
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 η, well understood in the framework on NLO QCD
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
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
ZEUS : Differential Open Charm Cross-Section
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
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
Karlheinz Meier - Kirchhof-Institut für Physik - Heidelberg University - Vth Workshop on Small-x and Diffractive Physics - Fermilab - September 2002
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.
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