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A network is proposed which comprises in an interactive manner all relevant projects in strangeness physics which deal with low energy antikaon-nucleon and –nucleus interaction studies, as well as investigations of the in-medium modification of the properties of antikaons and hyperons, including the still enigmatic deeply bound antikaonic nuclear clusters. Moreover, using the FAIR facility these studies will be extended to the charm sector and our goal is to extend our network in this sector too. It is our aim to promote this project as a centre of a worldwide extended network in this sector of strangeness physics, so including activities outside Europe, as for example those in Japan, considering European participation to the upcoming experiments at the JPARC facility in strangeness physics and the participation of Japanese groups in many of the European projects in the field.

The activities are concentrated on developing new strategies, both in experimental and theoretical sectors, to attack the still many open problems in the field. The development of new experimental methods and techniques (e.g. SDDs as high-performance X-ray detectors, GEM based detectors, detectors employing RPC’s and new SiPM photon detectors (see corresponding JRA proposals in HadronPhysics2) will greatly profit from this coordinated network. All major European institutes working in this field are participating to this network proposal, therefore a platform is given to strengthen and bundle the efforts. It is mostly important that young researchers will take advantage of the network. In general this proposal asks for a modest amount of funding but provides a big opportunity for the European research done at major European infrastructures, so that Europe becomes more and more the leader in the field.

An intensified collaboration of experimentalists with theoreticians, for the analysis of the new upcoming experimental results and their interpretation in the framework of the non-perturbative strangeness QCD is an essential goal of LEANNIS. This close collaboration between scientists will lead to a fast and efficient exchange of the latest results and ideas and will be decisive for the planning of future projects.

·         Definition and coordination of the scientific projects with the objective to obtain a more complete and deeper understanding of the low energy antikaon-nucleon and –nucleus interaction, of the in-medium properties of antikaons and hyperons, including possible formation of antikaonic nuclear bound states.

·         Coordination of the development of new experimental and theoretical methods as well as of the new scientific programs in the field of strangeness physics in order to setup a platform for the most efficient cooperation and use of the present and future European research infrastructures.

·         Provide Europe-wide exchange of young researchers in the field of strangeness physics.

·         Establish contacts and optimize the collaborative efforts for experiments at the non-European Research Facilities, such as those at J-PARC in Japan.

T1. Theoretical investigations in strangeness-nuclear physics

A key issue in the physics of the strong interaction is the dynamics driven by the chiral symmetry breaking scenario of low-energy QCD. Spontaneous chiral symmetry breaking with pions as Goldstone bosons governs the low-energy physics in the two-flavour sector of the lightest (up- and down-) quarks, while explicit symmetry breaking by the mass of the strange quark plays an important role when extending the framework to flavour SU(3). Low-energy interactions of antikaons with nucleons and nuclei, measured with the highest possible precision, are excellent probes to explore and improve the understanding of this fundamental issue: the entanglement of spontaneous and explicit chiral symmetry breaking.

High-precision K-p threshold data set important constraints for theoretical approaches and have recently been supplemented by the accurate results for kaonic hydrogen from the DEAR experiment. Various theoretical analyses point to questions of consistency of the recent DEAR data with previously measured sets of K-p scattering data. It is expected that SIDDHARTA (see T2) will improve the DEAR data further on and will attempt the very first measurement of kaonic deuterium which allows extracting, in principle, the two s-wave kaon-nucleon scattering lengths separately.

Accurate results for antikaon-N threshold data are a prerequisite for realistic studies of deeply bound antikaon-nuclear states. At present, various experimental results and first exploratory theoretical approaches do not yield a conclusive picture about the possible existence and properties of such deeply bound states. A systematic theoretical framework based on chiral effective field theory in combination with non-perturbative methods must be developed to provide a clean theoretical link to QCD. Such a framework will be the basis for unambiguous theoretical studies of K-pp clusters, antikaons in nuclear matter and antikaonic nuclei.

Leading roles in these investigations will play TUM and UBonn. They will use chiral SU(3) coupled channel dynamics and nested effective field theories.The University of Technology (Vienna) will support them in these activities, while SINS and UH will care about deeply bound K⁺ + (pp K-) reaction with the FOPI detector at the GSI accelerator facility in the 2.85- 3.30 GeV bombarding energy range. It is of utmost importance to perform these experiments at various bombarding energies for a clear separation of the two-body K⁺ (ppK^-) production channel from the three-body K⁺pΛ background channel, which is expected to be much larger in the pΛ invariant mass spectrum. The data taking starting in 2008/2009 is supposed to settle very clearly the existence of ppK^- states, and if so, the binding energy and the total and partial decay widths can be deduced.

The leading groups in this experiment are the Helmholtz Young Investigators Group from TU Munich and SMI in collaboration with groups from UHEI-PI and UW. The Helmholtz Young Investigators Group will build a TPC-prototype for the PANDA-experiment, which will be tested as a component of the pp2KΛp project.

T6. Search for kaonic nuclear clusters with COSY-TOF at FZ-Jülich

With its very large acceptance, full azimuthal symmetry, and good tracking capability close to the interaction point, the COSY-TOF detector is ideally suited to study final states with strangeness in proton-proton collisions. Presently the detector is being upgraded with an about 0.3 m³ volume straw tube tracking system which will further improve the tracking information, resulting in significantly better mass resolution for final state particles or two-particle systems as well as larger Λ, Σ, and K_S reconstruction efficiencies. As a side-aspect, the operation of the COSY-TOF straw tube detector will deliver useful information for the design of a straw tube tracking detector as one of the two options for the PANDA central tracking system.

At COSY-TOF the reaction pp ® ΛpK⁺ reaction can be measured in its full phase space essentially without background from much more copiously produced non-strange final states. A detailed study of this reaction will reveal the contribution of a bound ppK^- system formed as an intermediate state via pp ® (ppK^-)_bound K⁺ ® ΛpK⁺. Formation of a bound kaonic-two-proton state will be visible in a peak-like structure in the Λp invariant mass spectrum. The planned study of this reaction at the maximum energy of the external COSY proton beam of 2.55 GeV(3.35 GeV/c) is closely related to the program at FOPI at GSI (T.5) which focuses on the investigation of this reaction at higher incident energies. While the production cross sections are expected to be lower at lower beam energy, the COSY beam energy is still sufficient to kinematically cover the full Λp invariant mass spectrum from its threshold up to the ppK^- threshold, and thus includes the region where bound ppK^- states can be expected.

The experiment will be mainly performed by FZJ. The interpretation of the pp ® ΛpK⁺ data in all the relevant aspects outlined above will be based on a close cooperation with the theory groups of FZJ and UBonn.

T7. Search for kaonic nuclear clusters with stopped antikaon reactions (AMADEUS) at LNF-INFN

Upcoming are exclusive studies of the production and decay of kaonic nuclear clusters produced by stopped antikaon absorption at the DAФNE Ф-Factory at LNF in Frascati with the detection of all charged, and neutral outgoing particles including photons using the KLOE 4π- detector system, cryogenic targets and a kaon tagging system similar to SIDDHARTA. The deliverables will be, besides high statistics studies of various absorption processes of stopped antikaons in light nuclei, the possible unambiguous detection of various light antikaonic nuclear systems, such as ppK^-, ppnK^-, and pnnK^- with data on the binding energies, total widths and all partial decay widths. From Dalitz plots of their 3-body decays detailed structure information, such as parity, angular momentum, radii and densities can be deduced. Such data would give valuable input in theories for the description of dense and cold strongly interacting systems which are based on interactions studied by SIDDHARTA.

The experiments will be jointly performed by INFN-LNF and OeAW, supported theoretically by TUM.

T8. Antikaon nucleus potential in π-A reactions (FOPI) at GSI

The antikaon-nucleus potential at normal nuclear density will be extracted from a measurement of antikaons in pion induced reactions on nuclear targets with the FOPI detector. The analysis will be based on a direct comparison of the momentum spectra of kaons and antikaons and thus avoids many systematic biases. The interpretation of the data requires close collaboration with the theory groups.

The data taking, mainly by UHEI-PI and UW, is foreseen for 2009, data analysis and simulations will be done thereafter.

T9. Kaonic nuclear cluster search in heavy ion reactions at GSI

New high statistics data will be taken in 2008 and 2009 with the FOPI apparatus at GSI . Possibly formed multi-baryonic states are reconstructed in channels that contain charged particles only, like ppnK^- à Λ d. Highly compressed fireballs are predicted to represent unique conditions that could favor the production of deeply bound states. Since the optimal conditions are unknown so far, three different reactions will be measured: a medium-heavy symmetric system (Ni+Ni) at the highest possible energy at SIS18 (2AGeV), the heaviest possible system at 1.7 AGeV (Ru + Ru) and an asymmetric reaction(Ni+Nb) at the highest energy (2AGeV). The analyses aim at reconstructing Λ– hyperons and analyze the correlation with other ejectiles.

The experiment will be conducted by UHEI-PI and UW. The interpretation of the data will clearly benefit from the close interaction with theoreticians participating in the network.

T10. In-medium modifications of antikaons and D mesons (PANDA) at FAIR
The future PANDA program at FAIR contains various projects to study the in-medium modification of antikaons and charmed mesons following the antiproton annihilation in nuclei. Of particular interest are K- and D⁺-mesons. The D⁺-mesons contain besides the heavy charm quark light antiquarks like the K- -mesons, the in medium properties of which are studied by the AMADEUS and pp2KΛp projects. The connection of both phenomena is interesting because it reveals the dependence of hadron in-medium properties on the mass of the heavy quark.

During the duration of FP7, only preparatory work can be done, including work on the event generator, MC simulations and the development of nuclear targets. The experimental work will be mainly performed by OeAW, INFN-LNF, FZJ and the Helmholtz Young Investigator Group. Intense cooperation with theoretical groups is of great importance in assessing the sensitivity of experimental observables.

T11. Search for double antikaonic nuclei with antiproton annihilations (DAN) at FAIR
In antiproton annihilation in nuclei there is an exciting option to produce, in addition to single antikaonic nuclear clusters, also double antikaonic nuclei as has been proposed and found recently in antiproton annihilation data in helium. This may become a very powerful tool to produce very dense and cold matter in the future.The preparatory work will be done by OeAW.

The activities of the Network will produce intensive contacts between the infrastructures (LNF, GSI, COSY, J-PARC) working in the field of hadron physics with strange and charmed particles and the experimental and theoretical groups.

In particular the following questions will be addressed:

·         Precise determination of the isospin dependent antikaon-nucleon scattering lengths using kaonic atom X-ray spectroscopy followed by theoretical extraction and interpretation.

·         Precision X-ray spectroscopy of kaonic atoms with light nuclei, such as ³He and ⁴He for determination of the antikaon-nucleus interaction including its theoretical interpretation.

·         Antikaon-nucleon/nuclei “classical” physical processes, such as absorption and scattering, still poorly understood due to the lack of experimental results and, consequently, lack of precise theoretical analyses.

·         Disentangle the mystery of the Λ(1405) structure.

·         Study of the properties of excited Sigma states, such as Σ(1385) in the nuclear medium using p-induced reaction and (Lπ)- invariant mass spectroscopy.

·         Further developments and applications of theoretical methods: chiral perturbation theory, effective field theory with strangeness, chiral SU(3) dynamics with coupled channels, antikaon-nuclear few-body theory; comparisons with data from high-precision experiments.

·         Understanding the possible effects of strangeness in the interior of dense neutron stars.

·         Search for deeply bound antikaonic nuclear states using various reactions and fully exclusive determination of the reaction and decay products for determining of their masses, total widths, partialwidths, spins, parities and densities.

·         Search for double strange nuclear systems using antiproton induced annihilation reactions for the possible production of highly compressed low energy hadronic matter.

·         First studies of the properties of D⁺ mesons in the nuclear medium.