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Partonic Interpretation of Diffraction at HERA

Partonic Interpretation of Diffraction at HERA. C hristian Kiesling, MPI München. Introduction Experimental Methods General Features of Diffraction at HERA Partonic Structure from QCD Fits Tests of QCD Factorization Summary and Conclusions.

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Partonic Interpretation of Diffraction at HERA

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  1. Partonic Interpretation of Diffractionat HERA Christian Kiesling, MPI München Introduction Experimental MethodsGeneral Features of Diffraction at HERA Partonic Structure from QCD Fits Tests of QCD Factorization Summary and Conclusions C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  2. All total cross sectionsinvolving strongly interacting particles (hadrons)show approximate constancy, more precisely: universal slow rise, towards high energy Hera DL: Introduction „constant“ cross sections arise from Diffractive Phenomena Regge theory: trajectory in the t-channel vacuum QNE = „Pomeron“ QCD: colorless exchange Gluons, quarks in a color singlet ? What is diffraction in the partonic language ? C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  3. HERA – the world‘s largest electron microscope (Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany) HERA start: 1992 upgraded in 2001: „HERA II“ : 920 GeV : 27.5 GeV ~ 6.3 km circumference Resolution: ~ 10-18 m 50 TeV on stat. target C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  4. Diffraction in Interactions ES DVCS various phenomenological models: quasi-elastic VM prod. „ES“ Regge-motivated (factorizable Pomeron) Soft Color Interactions Color Dipole Models(2 gluon exchange models,saturation models) photondissoc. GD protondissoc. PD Diffraction very interesting wrt saturation:may be the first place where saturationshows up. DD C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  5. Rapidity Gap Method DIS event Diffractive Event Forw. Neutron C. Leading Proton Spectrometer Forw. Pr. Spect. Experimental Techniques Measuring the scattered proton C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  6. LPS Method proton scattered at small angles,measured in LPS,get longitudinal and transversemomentum components MX MethodQCD radiation suppressed between struck quark and protonremnant rapidity gap MX distribution flat in fit to non-diff mass distribution: Experimental Techniques (cont.) C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  7. (momentum transfer)2 virtuality of („size“ of the probe)-1 fraction of the proton momentum carried by the charged parton fraction of the electronenergy carried by the virtual photon („inelasticity“) color singletexchange center of mass energyof system (mass)2 of system Probing the Partonic Nature of Diffractive Exchange C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  8. momentum fraction of charged constituent of the diffractive exch., participating in the hard scattering (momentum transfer)2 at proton vertex Probing the Partonic Nature of Diffractive Exchange (cont.) momentum fraction of color singlet exchange relativeto the proton C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  9. universal, hard scattering cross section, calculable in pQCD diffractive PDF‘s of flavor in the proton, for fixed(evolves in Q2 according to DGLAP) ( can be neglected at low ) Diffractive Cross Sections and QCD Factorization (QCD) Factorization for diffractive scattering (Collins et al.): C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  10. shape of diffr. PDF‘s independent of Integration over (usually unobserved): Pomeron flux factor Regge Factorization Additional assumption (no proof): Regge factorization, the „Resolved Pomeron“ (Ingelman-Schlein-Model) normalization of controlled by Pomeron flux C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  11. Example: ZEUS LPS data Parameterization of Pomeron flux: Experimental Test of Regge Factorization at low : data support Regge factorizationhigher : sub-leading Reggeons necessary C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  12. Diffractive vs Inclusive DIS weak dependence on , similar to the photon (few partons ?) C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  13. Diffractive vs Inclusive DIS (cont.): Q2 dependence incl:scal. viol. ~ 0.15 diff:scal. viol. ~ 0.6 Positive scaling violations up to large : gluon-dominated („few“ gluons) C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  14. DIS region: same energy dependence(QCD-like, e.g. saturation models) Transition region: diffractive steeper than inclusive (Regge-like) Diffractive vs Inclusive DIS (cont.): W dependence C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  15. (using rapidity gap method) Statistics improved by a factor 5 ! (based on Forw. Proton Spect.) Agreement between both methods(similar results from ZEUS) With high precision data now DGLAP analysis possible (similar to DIS): partonic structure of diffraction Full HERA I data set (curves from QCD fit, see below) C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  16. (squared Chebychev polynomials (3 params) times exponential damping for ) Partonic Structure of Diffraction: (LO, NLO DGLAP fits) NLO LO ansatz for the partonic structure: charm via boson gluon fusion via QCD relation NLO DGLAP fit for singlet and gluoncontributions to C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  17. restrict data to (pomeron factorization holds) positive scaling violations even for large  : gluon dominates Partonic Structure of Diffraction (cont.) gluon distribition mainly determined from scaling violations C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  18. Gluon momentum fraction: Partonic Structure of Diffraction (cont.) Full propagation of experimental uncertainties (inner error bands) Theoretical uncertainties (outer bands): Diffraction is gluon-dominated C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  19. di-jets charmproduction jet 1 jet 2 sensitive to the gluon content photon virtuality cms emergymass of diffr. System inv. 2-jet mass Detailed Tests of the Partonic Picture test QCD factorization using diffractive pdf‘s LO:higher order: momentum fractioncarried by pomeron momentum fractioncarried by the partoninside the pomeronentering the hardsubprocess C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  20. new cuts w.r.t. published data (Eur. Phys. J. C20 (2001) 29) (NLO unstable if ) measure directly from identified jets (CDF cone algo.) NLO calculations using DISENT compare with MC predictions using gluon from H1-QCD fit to inclusive data Dijets in DIS Diffractive Scattering correction to hadron level applied NLO calculations agree with data – factorization seems to work C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  21. (suppress subleading Reggeon exchange) Charm Production in Diffraction Charm directly probes the gluonic component of the Pomeronvery sensitive to different dpdf‘s data still statistics limited C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  22. Charm rate independent of also for charm factorization seems to work Charm Production in Diffraction (cont.) Predictions: use gluon pdf from a NLO QCD fit(Alvero et al.)to inclusive diffractive data (similar to the H1 fit) data well described, both by QCD model (HVQDIS, Harris et al.) in addition (not shown): (Charm not suppressed in diffraction) C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  23. Further Tests of QCD Factorization in Diffraction One step further: use dpdf‘s to predict di-jets at the Tevatron Observe serious breakdownof factorization: Prediction from HERA an order of magnitude too large Generally for Tevatron: Also other diffractive processesonly of order 1 % Possible reason: additional hadronin the initial state, rescattering,reduction of „gap survival probability“(Kaidalov, Khoze et al.) C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  24. Further Tests (cont.): Di-Jets in Diffractive Photoproduction low virtuality photons at HERA are „hadrons“ LO MC (Rapgap) with dpdf from H1 fit does describe the data ! No violation of factorizationin „hadron physics“ at HERA ? C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  25. Factorization Tests in Diffractive Photoproduction (cont.) NLO calculation by Klasen & Kramer (2004)resolved photon contributions: factor ~ 3 reduction seems to match with the data (absorption correction suggested by Kaidalov, Khoze et al., 2003) C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  26. Strong experimental evidence for gluonic structure of diffractive exchangeNLO QCD fit to diffractive data: gluons dominate (~75%). QCD factorization verified at HERA in diffractive DIS (di-jets, charm) Strong breaking of factorization seen with di-jets at the Tevatron, LO/NLO predictions for HERA photoproduction of di-jets possibly not yet fully understood Diffraction (color singlet exchange) continues to be a major challengefor QCD and, possibly, is a key to understand confinement QCD models based on 2-gluon exchange seem to describe the hard-scale diffractive processes, Regge picture fails in diffractive DIS Summary and Conclusions Diffraction phenomena govern the main part of the cross section insoft hadronic interactions and, surprisingly (?), a substantial part of hard scattering at HERA C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  27. BACKup C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  28. C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  29. using improved Forward Calorimeter Leading Proton Spectrometer data: (transition region to photoproduction) measurements by ZEUS C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  30. Dijets in DIS Diffractive Scattering (cont.) C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  31. Regge picture Total cross sections for photoproductionof vector mesons: r , w , f show Regge behaviour J/ynot described by Regge, strong rise of cross section Break-down of Pomeron Universality Photoproduction of Vector Mesons C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  32. Odderon invented by Lukaszuk and Nicolescu (1973) to account for possible differencesin hadron-hadron and antihadron-hadron scatteringat high energies If B non-zero at high energies,i.e. a diffractive amplitude: for A B + A B Experimental difficulties(due to presence of the Pomeron): Subtraction of 2 large numbers - No data on at high energy ! Theoretical problem: Odderon possibly suppressed in reactions The Odderon B is „odd“under charge conjugation C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  33. The „Odderon“ is a firm prediction from pQCD: 3-gluon state with C = P = -1 (see talk by C. Ewerz) HERA is an ideal place to study the Odderon: very high photon-proton center-of-mass energies (up to 300 GeV) can select exculsive processes where the Pomeron cannot contribute (thus measure a potential Odderon contribution directly, no subtraction) theoretical (non-pQCD) modelexist for exclusive processes: E. R. Berger, A. Donnachie, H.G. Dosch, W. Kilian, O. Nachtmann, M. Rueter Cross section NOTsuppressed if state Xis a negative-paritybaryon (e.g. ) Cross sections foran order of magnitude smaller Do we need an Odderon ? If so, how to find it : C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  34. to test the diffractive nature of Odderon need large photon-proton energy(meson is emitted into backward part of detector) low mass mesons deposit all their energy in backward region of detector no tracking detector in backward area photons give full energy calorimetric measurement (VLQ, SpaCal) Diplomathesis ofT.Golling Reactions investigated: PhD Thesisof T. Berndt Odderon Search in Multi-Photon Final States Why multi-photon final states ? C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  35. Exclusive Photoproduction (neutron detected in forward calorimeter) (photoproduction, energy measured via e-tagger) (photons detected in VLQ and SpaCal) Spa FNC VLQ H1 VLQ E-tag Cal Neutrondetector(calorimeter) Photon energyvia measurement of scatteredelectron No charged particles: nominal interaction point used as origin of photons C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  36. Exclusive Photoproduction (cont.) • After cuts against „inelastic“ events some events remain, compatible with expected background • Expected signal from Berger et al. model is not seen • H1 is able to detect 0in VLQ/SpaCal • Neutrons can be detected with good efficiency (signaling N* production) • Acceptance/efficiencies are under control C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  37. <W> = 215 GeV 95 % C.L. 200 nb expected for diffractive Odderon in same kinematic range ( ) Interpretation of result: Odderon-photon coupling could be smaller than in Berger et. al. Odderon intercept is smaller than 0.7 (no longer „diffractive“) Limit on Exclusive Photoproduction Event distribution as functionof the momentum transferat the proton vertex. Reason: limited acceptance (goes to 0 as t approaches 0, small for |t | > 0.5 ) Cross section limit given in range 0.02 < |t | < 0.3 GeV2 C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  38. A 2-gluon color singlet state („Pomeron“) with C=P=+1 seems firmly established in strong interactions to mediate diffractive phenomena,most importantly to produce constant cross sections („BFKL Pomeron“) The C=P=-1 3-gluon color singlet state („Odderon“) is a natural extensionof this idea. Detection of Odderon usually plagued by presence of the dominating „background“ from the Pomeron („subtraction of big numbers“) HERA provides a unique possibility to directly measure the Odderon(exclude Pomeron explicitly by quantum numbers), reliable (factor 2) non-perturbative calculations exist. BUT: No signal found yet ! More Data !! HERA II (new VFPS) Charge/spin asymmetriesin 2-pion photoproduction(at HERA II) interference effects C=+1 C=-1 Summary on the Odderon How to continue ? Recent suggestion(Teryaev et al. ICHEP 2002) C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

  39. C. Kiesling, ISMD 2004, July 26-31, 2004, Sonoma State University, California, USA

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