Study the feasibility of an electron-nucleon collider (ENC) as a future extension of the HESR at the FAIR facility.

Description of work and role of partners
The main objective of the EPOS network is to foster the interchange of ideas and methods in non-perturbative QCD and their applications to hadron and nuclear phenomenology, including also few- and many-hadron systems. This is intimately linked to the on-going experimental efforts at COMPASS (CERN), COSY (Juelich), DAPHNE (Frascati), ELSA (Bonn), GSI (Darmstadt) and MAMI (Mainz) for light quark systems and at BELLE (KEK), BES (Beijing) and CLEO (Cornell) for systems with light and/or heavy quarks, and in the future J-PARC, LHCb and FAIR.

A second objective is to prepare methods to make best use of the upcoming FAIR facility at Darmstadt but also to provide new methods to attack problems that were believed so far to be too difficult to handle like e.g. CP-violation in D-meson decays. Such precision tools will also allow to set limits on possible physics beyond the Standard Model. A reoccurring theme will be to investigate the structure of the observed hadrons and trying to unravel their true nature (conventional 3-quark or quark-antiquark states, hadronic molecules, multi- quark states, …..). Again, theoretical tools will be developed to make such identifications possible and unambiguous.

The physics issues pertinent to the EPOS network can be grouped into four majors tasks:

  1. Precision calculations in strong interaction physics will focus on the refinement and application of effective field theories (EFTs) like chiral perturbation theory or nuclear effective field theory, eventually supplemented with unitarization methods and dispersive techniques. Some central issues will be a detailed analysis of (1232) effects in photo-nucleon and nuclear processes, precision calculations of pion-pion, pion-kaon and pion-nucleon scattering, a systematic analysis of two-photon exchange effects, and the development of new Dalitz-plot methods to extract CP-violation from D-meson decays. Further, non-relativistic EFTs will be refined and applied to the extraction of hadronic scattering lengths from mesonic three-body decays.
  2. Multi-quark and multi-hadron states will focus on the spectrum of QCD, in particular on the many exciting data in the charm quark region, and provide refined tools to analyze these. Here, a comprehensive study of hadronic molecules and of three-hadron states as well as multi-quark states within covariant quark models will be performed. In particular, a quantitative understanding of the charmonium spectrum, the charm strange mesons and the many X, Y, Z states is aimed at, with predictions on their decay patterns that can be tested e.g. in future experimental facilities. The structure of the scalar mesons as revealed in photo-nucleon processes will be scrutinized. Further, the role of universality for weakly bound compounds will be scrutinized.
  3. Lattice methods and applications will have two main foci. First, finite volume methods will be developed that allow for a systematic study of hadron resonances and their properties from lattice QCD data at sufficiently small quarks masses, supplemented with the corresponding chiral extrapolations. In particular, the lowest lying nucleon excitations P11 and S11 will be studied in large volumes close to the physical mass. Second, nuclear lattice simulations that combine EFT and MC simulation methods will be used to perform ab initio calculation of light and medium-heavy nuclei. These developments will open new and exciting possibilities of studying the two manifestations of strong QCD that so far could not be investigated quantitatively.
  4. Nuclear matter and phases of QCD will focus on new developments for dense and hot QCD that are directly linked to the methods developed in EPOS and its predecessors. Effective field theories will be applied to the nuclear energy density functional and to nuclear and neutron matter to finally achieve a true understanding of the nuclear equation of state, in particular its saturation properties. Further, the PNJL model will be used to study aspects of the hadron to quark transition in hot QCD matter, in particular the role of multi-quark interactions and the possible emergence of exotic phases of QCD. Lattice QCD will be used to study the order of the phase transition at non-zero temperature near the physical point.

Participants and their qualifications
The following institutions will participate in this network: 26 institutions from 12 countries with about 100 permanent researchers, about 45 post-docs and about 65 students. This amounts approximately to a total 90 FTE. The various institutions are engaged in the tasks given in the table, based on their qualifications in the various fields:
U. Bonn, Germany (Ulf-G. Meißner) Task: 1, 2, 3, 4
TU Muenchen, Germany (Norbert Kaiser) Task: 1, 2, 3, 4
U. Mainz, Germany (Marc Vanderhaeghen) Task: 1, 2, 3, 4
U. Bochum, Germany (Evgeny Epelbaum) Task: 1, 3, 4
U. Tuebingen, Germany (Amand Faeßler) Task: 1, 2
U. Gießen, Germany (Ulrich Mosel) Task: 1, 4
FZ Juelich, Germany (Christoph Hanhart) Task: 1, 2, 4
GSI Darmstadt, Germany (Matthias Lutz) Task: 1, 2, 3
U. Graz, Austria (Reinhard Alkofer) Task: 1, 2, 3
U. Valencia, Spain (Eulogio Oset) Task: 1, 2, 4
U. Barcelona, Spain (Angels Ramos) Task: 2, 3, 4
U. Granada, Spain (Carmen Garcia-Recio) Task: 2, 4
U. Madrid, Spain (José Pelaez) Task: 1, 2, 3
U. Salamanca, Spain (Francisco Fernandez) Task: 2
U. Murcia, Spain (José Oller) Task: 1, 2, 4
U. Paris-Sud, France (Bachir Moussallam) Task: 1, 3
CPT Marseille, France (Marc Knecht) Task: 1
U. Pavia, Italy (Barbara Pasquini) Task: 1, 2
U. Manchster, United Kingdom (Mike Birse) Task: 1, 4
U. Cracow, Poland (Henryk Witala) Task: 1, 4
U. Lund, Sweden (Johan Bijnens) Task: 1
U. Bern, Switzerland (Gilberto Colangelo) Task: 1, 3
U. Coimbra, Portugal (Brigitte Hiller) Task: 4
IST Lisbon, Portugal (Teresa Pena) Task: 1, 2
ITEP Moscow, Russia (Boris Ioffe) Task: 1
ODTU Ankara, Turkey (Altug Ozpineci) Task: 2

1: precision calculations; 2: multi-quark and multi-hadron states; 3: lattice methods and applications; 4 nuclear matter.accordingly.