odderon searches and hadronic final states in diffractive scattering at hera karlheinz meier

$: Odderon Searches and Hadronic Final States in Diffractive Scattering at HERA Karlheinz Meier$
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


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





W (p mass)





?


H1 : Excl. Meson Production via C = +1 and C = -1 Exchange

Idea : Unambiguous measurement of final state charge conjugation Clook into pure photonic decays, count photonsODD number photons means POMERON exchangeEVEN number of photons means ODDERON exchange

„2 gluons“ C = +1

1 photon C = -1

„3 gluons“ C = -1


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


JPC Mass (MeV/c2)Γ (MeV /c2)

Predicted σp

exchane2 cluσtereventσ

3 cluσtereventσ

4 cluσtereventσ

5 cluσtereventσ

p° → BR = 1

0 − + 139.67.7 ⋅ 10-6

200 nbOdderon

SinalChann el

neliible neliible neliible

ω° → p° → BR = 0.085 ⋅ 1

1 − − 782.68.44

300 nbPom eron

neliibleSinalChann el neliible neliible

f2 → p°p° → BR = 0.282 ⋅ 1 ⋅ 1

2 + + 1275.4185.1

21 nbOdderon

neliible neliible SinalChann el

neliible

a2 → p°h → BR = 0.145 ⋅ 1 ⋅ 0.393

2 + + 1318.0107

190 nbOdderon

neliible neliibleSinalChann el

neliible

ω°p° → BR = 0.085 ⋅ 1⋅ 1

1 + − non reσonant 1200 nbPom eron

neliible Backround Backround SinalChann el

b1 → ω°p° → BR = 1⋅ 0.085 ⋅ 1⋅ 1

1 + − 1229.5142

600 nbPom eron

neliible Backround Backround SinalChann el

H1 : Expected Signals, Backgrounds and Topologies


Search for Odderon-Induced Contributions to Exclusive p° Photoproduction at HERAH1 Collaboration, C. Adloff et al., Phys. Lett. B544

H1 : Excl. p° 2 Production (C = -1 Exchange, Odderon)

no signal observed, limit at 95% C.L.σ(p) p° + 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 p° is clearly seen at correct rate


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).


= 4.95 nb-1

clear intermediate p° signal seen and used for event selection


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


= 4.95 nb-1

p° mass windows used for event selection


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


= 4.95 nb-1

p° and h mass windows used for event selection


H1 : Excl. p°ω°(b1) 5 Production (C = +1 Exchange, Pomeron)

clear signal observedσ(p) ω° + p° + X + X = 980 200 (stat.) 200 (sys.) nbcompatible with dominant resonant part from b1 ω° + p° (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))


= 4.95 pb-1

p° and ω° mass windows used for event selection


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





W (p mass)






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)





W (p mass)






H1 : Diffractive 2-Jet Production in Deep Inelastic Scattering

Data from H1 Eur.Phys.J. C20 (2001)

4 < Q2 < 80 GeV2

Use both, NLO (as2) 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


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


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.


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


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


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


ZEUS : Diffractive D* Production in Deep Inelastic Scattering

DESY-03-094

1.5 < Q2 < 200 GeV2

0.02 < y < 0.7

XP < 0.035

b < 0.8

pT(D*) > 1.5 GeV

|h(D*)| < 1.5

Signal of 4976 103 Mesons

(cross section 0.521 nb)


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 h, well understood in the framework on NLO QCD


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


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


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.

odderon searches and hadronic final states in diffractive scattering at hera karlheinz meier

Documents

angular momentum

production c

herez momentum fraction

pomeronq2 momentum transfer

odderon exchange2 gluons

exclusive meson production

exclusive photoproduction

j production