European Network

Hadronic Physics with High Energy Electromagnetic Probes (HaPHEEP)


This is the WWW server of the European Network Hadronic Physics with High Energy Electromagnetic Probes. The network consists of 12 participating organizations, cf. the clickable map below the main directory.

This network is funded by the European Commission's 4th Framework Training and Mobility of Researchers programme. The network contract (ERBFMRXCT96-0008) was concluded between the European Commission and the participants on 1 August 1996 with a duration of 48 months. Further details on the TMR programme and other networks may be found at

Main Directory:

- Latest News NEW new network ESOP approved

- Research Objectives

- Training Content

- Management

- Major Tasks:

- Semi-Inclusive Reactions
- Exclusive Reactions
- Real Photons and Spin, have a look at the Report of the European Real Photon Working Group

- Calendar: Future meetings, Past meetings


- Reports
- useful links NEW


Click on the map to find information about the participating organizations:


Latest News

The application for an extension of the duration of the network to 4 years was approved.
Therefore, the end of the network will be end of July, 2000.

NEW New network ESOP approved

The Network ESOP (Electron Scattering Off Confined Partons) has been approved by EC (European Commission), and the Contract is under negotiation.

The Network will provide a forum where European researchers will prepare their future by strengthening existing collaborations, initiating new collaborations and training young researchers who will become leaders in the field. It gathers theoreticians and experimentalists, as well as Nuclear and Particle Physicists.

The research objectives are:

  1. to decipher the spin and flavour structure of hadrons,
  2. to determine parton structure functions and distributions --with a special emphasis on Off Forward Parton Distributions (OFPD's)--
  3. to set the scientific background for future facilities.
Experiments and theoretical efforts will be combined. The experiments will be carried out at top nuclear and particle facilities (MAMI, HERMES, COMPASS, JLab), and the theoretical support will be led by world experts.

First announcement of postdoc positions in the ESOP network.


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Research Objectives

Quark confinement is still an open problem in the study of the structure of hadronic systems within Quantum Chromodynamics. Its solution calls for subtle measurements, where spin degrees of freedom and the selection of specific final state configurations are key ingredients. New technical developments (polarized electron beams of high intensity and duty factor, high quality detectors, ...) meet this demand, but the scale of collaboration outgrows national efforts, such as presently at NIKHEF, Mainz, Bonn, or Grenoble, and calls for a European effort.

This network will provide a forum where experimentalists and theorists will combine their expertise. It will enlarge and strengthen collaborations already investigating this field at existing facilities. Three tasks have been identified: The study of the space-time evolution of elementary hadronic systems, via semi-inclusive reactions; The determination of the simplest components of the wave function of hadronic systems, via exclusive reactions; The study of the spin structure of hadronic systems, using polarized beams and polarized targets.

Training Content

The network strongly emphasizes the training of young researchers, giving them the opportunity to work together with world experts in an enlarged community. It includes the centers that play a leading rôle in the field. It is geographically balanced, including teams from the less favoured regions of Europe.

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Network coordinator:

Steering Committee:

Team contact persons

  1. J.-M. Laget (Saclay),,
  2. J. van de Wiele (Orsay),,
  3. R.E. van de Vyver (Gent),,
  4. P.J. Mulders (Amsterdam),,
  5. C.N. Papanicolas (Athens),,
  6. H.-J. Pirner (Heidelberg),,
  7. P. Kroll (Wuppertal),,
  8. E. de Sanctis (Frascati),,
  9. S. Boffi (Pavia),,
  10. B. Webber (Cambridge),,
  11. P. Hoyer (Copenhagen),,
  12. S. Noguera (Valencia),,
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Major Tasks:

The project has been broken up into three main tasks. When a team is involved in more than one task, its name appears in italics next to the tasks where its effort is less important. The major milestones are indicated for each task.

  • Semi-Inclusive Reactions
  • The first task is the study of semi-inclusive reactions. Here the photon hits a quark which subsequently hadronizes: one of the leading particles in the corresponding jet is detected in coincidence with the scattered lepton. This gives access to mechanisms which govern the evolution from a valence quark to a constituent quark and finally to the detected hadron. Some information on the quark fragmentation functions has already been obtained in the study of semi-inclusive reactions on a free nucleon. Special emphasis on polarized nucleon targets is needed. For a nuclear target, semi-inclusive meson electroproduction on nuclei will provide a microscopic detector to see how quark hadronization occurs in hadronic matter by selecting each step of color neutralization. In addition, one can envisage semi-inclusive reactions with the hadron detected in the target region.

    In order to perform a meaningful study, a sufficiently large kinematics range (minimum rapidity region) must be available. This limits the energy range of the leptons to around 30 GeV or higher. However, the study of the color interaction in the hadronic target (for instance, higher twist contributions which are suppressed as 1/Q^n or hadronization in nuclei) cannot be performed at energies much higher than 30 GeV. This is precisely the energy range of the HERMES set-up at HERA, which to date provides us with an opportunity to make a first incursion in this field. The first stage of the HERMES experiment (spin structure of the nucleon) starts in the spring 1995 and will last until the end of 1996 or the beginning of 1997. The second stage (nuclear targets) is under discussion and will cover the period 1997-1999. Teams of the proposed network are already participating to the HERMES collaboration, with a leading rôle. The theoretical component of the network will provide the framework to analyze these experiments, with a special emphasis on higher twist contributions, quark correlations, quark hadronization in nuclei and spin responses of nuclear matter. (Amsterdam, Cambridge, Heidelberg, Athens, Gent, Pavia, Frascati).

    Rainer Jakob (Pavia) has assembled a collection of information related to fragmentation functions.

  • Exclusive Reactions
  • The second task, which appears to be promising, is the study of exclusive reactions induced, on nucleon and nuclei, by electrons and photons at high momentum transfer (in the range 10-20 GeV^2 and above). These measurements select the simplest component (three valence current quarks of a baryon, a current quark-antiquark pair of a meson) of the wave function of a hadron. The corresponding hard mechanisms can be disentangled from the soft mechanisms which confine the quarks in the hadron ground or excited state. The study of several channels (elastic and inelastic nucleon form factors, Compton scattering, meson electroproduction, ...), with a special emphasis on spin observables, will lead to a better understanding of this simple valence quark component of the wave function. In the heavy quark sector (strange or charmed) exclusive measurements give access to more complicated components. In addition to the valence quarks, the possible presence of heavy q\overline{q} pairs is interesting; very important also are the gluonic components that can be studied in this way. Electroproduction of J/Psi or phi is particularly appealing in this respect. The study of these exclusive reactions in nuclei will allow us to see how these simplest configurations evolve to the wave function of a physical hadron: how current quarks dress themselves to make hadrons. This will be revealed through the "color transparency" mechanism.

    The determination of the cross-sections of such exclusive channels requires intense and continuous beams of electrons, in the range 15-30 GeV. To date, existing machines have too low an energy to guarantee the hardness of the elementary processes, but provide us with an opportunity to enter into this field. At low energy, these reactions are already accessible at Grenoble, Bonn, Mainz and Amsterdam (Compton scattering, meson production, ...). At higher energy, European teams are leading experiments at CEBAF (Compton scattering, vector meson production, baryonic resonance production, ...) which are scheduled in the period 1996-1999. On the theoretical side, the battery of analytical and numerical techniques, necessary to map out the hadron wave function from these exclusive reactions, will be developed. This includes calculations of exclusive cross-sections in the light cone formalism, investigations of ways to approach confinement (quark-diquark models, QCD sum-rules, etc...), as well as treatments of color transparency. (Wuppertal, Athens, Gent, Pavia, Saclay, Copenhagen, Valencia, Orsay, Amsterdam, Cambridge, Frascati).

  • Real Photons and Spin
  • The third task is the study of reactions induced by real photons. This is a useful complement to electron or muon scattering. On the one hand, the spin structure of real photon amplitudes is simpler (the photon can only be transversely polarized): a combined use of polarized photon beams and polarized targets allows a full determination of the helicity amplitudes. On the other hand, the energy of a real photon beam can reach the maximum energy of a given machine and allow us to reach kinematical domains inaccessible to electrons. Finally, the determination of the cross-sections at the real photon point appears to be a strong constraint on the models. Real photon beams already exist at Bonn and Mainz. A fully (linearly or circularly) polarized photon beam will be available at Grenoble (GRAAL) in summer 1995. At higher energy, CEBAF will provide a real photon beam in 1997. By the end of 1997, one may expect to have a full set of observables concerning kaon and eta meson production up to photon energy around 2 GeV. Teams in the proposed network belong to European collaborations which are being formed in order to verify the Gerasimov-Drell-Hearn sum rule, combining the potential of the Bonn, Grenoble and Mainz facilities, in the period 1997-1999. Groups in the network will also investigate ways to improve monochromatic photon sources, in view of their use at higher energy. On the theoretical side the collaboration will provide the tools to analyze these experiments. (Orsay, Frascati, Gent, Saclay).
    These three tasks represent three complementary ways to attack the problem of the short distance structure of hadronic matter. Collaboration of teams which have already made significant contributions to the field is mandatory to address such a challenging issue, and is the optimal place to train researchers entering in this area.

    A decision concerning the ELFE project (Electron Laboratory For Europe) is expected to be taken end of 1997. Most of the teams are involved in the preparation of this decision. Their collaboration and the results they will obtain at present facilities will certainly strengthen the case.


    1. "First European Workshop on Hadronic Physics in the 1990's with MultiGeV Electrons". Edited by B.Frois, D. Goutte, P.J. Mulders and P.K. De Witt-Huberts. Nuclear Physics A497 (1989) 1c-606c.
    2. "European Workshop on Hadronic physics with Electrons beyond 10 GeV". Edited by B. Frois and J.F. Mathiot. Nuclear Physics A532 (1991) 1c-582c.
    3. "1991 EPS Nuclear Physics Conference on Hadronic Structure and Electroweak Interactions". Edited by J.J. Engelen, J.H. Koch and P.K. De Witt-Huberts. Nuclear Physics A546 (1992) 1c-489c.
    4. "The ELFE Project, an Electron Laboratory for Europe", edited by J. Arvieux and E. De Sanctis, Conference Proceedings of the Italian Physical Society 44 (1993).
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    The following annual reports are now available:

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    some useful links to related sites:

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    These pages were designed by Daniel Boer, and are currently maintained by Rainer Jakob, member of team 7, Wuppertal.
    Sent mail to: Comments are appreciated.

    Last modified: Tue Feb 8 09:45:56 METDST