The central objectives of the proposed networking activity LEANNIS are the definition and coordination of studies on low-energy antikaon nucleon (nucleus) interaction in theory and experiment centered in Europe, but with strong impact on the worldwide strategy in the field.

 Description of work and role of partners

The proposed upgraded LEANNIS network will concentrate on hot topics in low-energy antikaon interactions with nucleons and nuclei to be studied in theory and experiment. It will take advantage of the basis created in the running LEANNIS network-project and of its outcome. Six main topics have been identified and are discussed in the following.

The participation of the subgroups is detailed below.

TP1. Theoretical investigations in strangeness nuclear physics
From the studies of hadron interactions substantial knowledge about the strong force and the underlying QCD theory can be obtained. In particular, the non-perturbative regime of QCD represents an extremely important scientific case for the understanding of matter. The role of strangeness in nuclear physics is still under intense investigations. Hadronic atoms with strangeness can provide important input for theoretical descriptions of the strong interaction at lowest energy. Effective field theories supplemented by phenomenological models have been developed and can be checked with high precision data from kaonic atom studies and with low energy Kˉ proton scattering experiments and reaction studies. The special case of the lively debated kaonic nuclear clusters (kaonic nuclei) is an integrated part of the proposed theoretical investigations. There are also strong connections with astrophysics, which we plan to further explore. A further fundamental question is the nature of the s-wave resonance Λ(1405). In the next decade PANDA at FAIR is supposed to start operation. Within the PANDA physics program possible modifications of hadron spectral functions, indicating changes of mass and decay width in nuclear matter, are investigated. In the preparatory phase of PANDA theory can contribute extensively to tailor and optimize the PANDA physics program. The field of strange exotic atoms and nuclei demands a joint effort of theory and experiment - therefore this close collaboration will be a cornerstone of the proposed network.

TP2. New precision studies of the strong interaction in kaonic atoms
In the last few years, new experiments on the strong interaction parameters in kaonic atoms took place. In spite of the success concerning kaonic hydrogen and helium, there is still the lack of crucial information about kaonic deuterium and some heavier kaonic atoms. New experimental programs are in preparation at LNF and (with participation of European researchers) at J-PARC. SIDDHARTA-2 at LNF has a broad spectrum of research topics, including the X-ray spectroscopy of the Lyman transitions in kaonic deuterium and helium. In addition,an experimental program is planned at DAΦNE to study with low energy K+ and K- beams scattering-and reaction-channels on protons and deuterons. Here, active hydrogen or deuterium targets in a TPC placed in the magnetic field of the KLOE detector at LNF will be used.

TP3. The nature of Λ(1405) by experimental investigations
For the understanding of the low-energy antikaon-nucleon interaction the sub-threshold resonances Σ(1385) and the famous and heavily discussed Λ(1405) are under investigation of current research. First results have already been achieved from the analysis of the HADES data from p+p collisions at 3.5 GeV. A similar analysis is currently being pursued for the measured p+p reactions at 3.1GeV with the FOPI detector at GSI. Within SIDDHARTA-2 the decay (Kˉp) Atom → γΛ* by γ-ray detection is planned for a direct study of the Λ*. Other direct studies concern pion induced reactions using the HADES and the FOPI detectors at GSI and kaon induced reactions on a deuterium target at J-PARC.

TP4. Search for kaonic nuclear clusters in dedicated experiments
A hot scientific case is the question on possible production mechanisms and properties (decay width, density) of kaonic nuclear systems bound by the strong force. Recently, the analysis of data from the DISTO experiment indicated the possible production of such systems in proton-proton collisions. In the timeline of LEANNIS experiments on this topic will be performed or prepared at LNF (AMADEUS), at J-PARC (E15), at GSI (FOPI and HADES) and at AD-CERN using complementary approaches: AMADEUS will be a laboratory for studying the antikaonic nuclei produced with stopped antikaons, E15 will measure Kˉ in-flight reactions. FOPI will continue to study pp reactions for the production of antikaonic nuclei. Studies on antikaons in nuclei and the search for multi-antikaon nuclear systems with slow antiprotons are planned for J-PARC and AD-CERN with the opportunity to continue at FLAIR at FAIR in the future.

TP5. Toward in-medium modification studies of charmed hadronic systems with PANDA at FAIR
At J-PARC the study of in-medium modification of φ- mesons is planned using antiproton beams. The in-medium modification of charmed systems like D-mesons is presently a “terra incognita”. Therefore, one of the main research fields of the PANDA experiment at FAIR is the study of such in-medium effects (see PANDA Physics Book). In the preparation phase of PANDA Monte-Carlo studies using crucial input from theory will be conducted in order to optimize the sensitivity of the experiment.
TP6. Expert Meetings, Workshops, Dissemination
All participants of LEANNIS will participate in these meetings which represent milestones reflecting the progress and the planned further activities. Special activities will be devoted to disseminate the results towards the general public.

Andrej Soltan Institute, Poland (TP1, TP3, TP6)
Forschungszentrum Juelich, Germany (TP4, TP5, TP6)
INFN-LNF, Italy (TP2, TP3, TP4, TP6)
Austrian Academy of Sciences (TP2, TP3, TP4, TP5, TP6)
Technical Univ. Munich (TUM), Germany (TP1, TP5, TP6)
Excellence Cluster Universe of TUM (TP2, TP3, TP4, TP6)
Universitaet Bonn, Germany (TP1, TP6)
Universitaet Heidelberg, Germany (TP4, TP6)
University Warsaw, Poland (TP4, TP6)