Search

The search for a quasi bound η meson in atomic nuclei is reviewed. This tentative state is studied theoretically as well as experimentally. OA gold

The past year 2006 has been a very successful one for the institute: first off, a major milestone has been achieved with the in-time installation of the WASA detector at an internal target station of COSY and its subsequent commissioning. WASA-at-COSY is ready to take data and the collaboration is looking forward to its first data production run, approved by the COSY-PAC and scheduled for spring 2007. Furthermore, after very productive scientific programs, the internal experiment COSY-11 and the external beam experiments at BIG KARL have finished their data taking phases, and are now completing the analysis of the existing data. The following highlights top the list of the important scientific results: • Pentaquark studies: the TOF-collaboration has very carefully analysed their dedicated high-statistics data sample, and did not find a signal for the $\circleddash^{+}$(1540). This finding has been supported by the ANKE-collaboration in a different final state. • Bound $\eta$-nucleus states: data with unprecedented precision for the $^{3}He\eta$ system have been obtained both at ANKE and at COSY-11 in the d p-reaction, exploiting the unique possibilities at the internal COSY beam during the ramp-up of the energy. The very rapid rise of the total cross section close to threshold implies a very large $^{3}He\eta$ scattering length and hence the presence of a quasi-bound state extremely close to threshold. • Hyperon-nucleon interactions: chiral effective field theory has successfully been applied to the interactions between nucleons and hyperons. This paves the way to a model-independent approach of strange quark effects in nuclei. • Accelerator studies: the COSY accelerator has been used for spin manipulations of a polarized deuteron beam, and clear indications for a deuteron spin resonance have been obtained. All results mentioned have recently been submitted for publication. More details and further results can be found in the main text. In addition to WASA, the two other major installations continue to be developed further: [...]

We present the results of a Bayesian analysis of a Regge model to describe the background contribution for K+ Lambda and K+ Sigma0 photoproduction. The model is based on the exchange of K+(494) and K*+(892) trajectories in the t-channel. We utilise the Bayesian evidence Z to determine the best model variant for each channel. The Bayesian evidence integrals were calculated using the Nested Sampling algorithm. For different prior widths, we find decisive Bayesian evidence (\Delta ln Z ~ 24) for a K+ Lambda photoproduction Regge model with a positive vector coupling and a negative tensor coupling constant for the K*+(892) trajectory, and a rotating phase factor for both trajectories. Using the chi^2 minimisation method, one could not draw this conclusion from the same dataset. For the K+ Sigma0 photoproduction Regge model, on the other hand, the difference between the evidence integrals is insufficient to pinpoint one model variant., Comment: 13 pages, 4 figures

The IKP has achieved a strategic success in 2009: the proposal of the IKP for funding in the Research Program Physics of Hadrons and Nuclei, defined in the framework of the Program Oriented Funding of the Helmholtz centers, has been evaluated in February with great success. This decision guarantees the funding of IKP as well as those parts of ZAT and ZEL participating in the proposal for the time period from 2010 till 2014. The following outstanding experimental results have been obtained: • The WASA at COSY collaboration has used the pd $\rightarrow$ $^{3}$He $\eta$ reaction to accumulate 30 million $\eta$-meson decays, obtaining clear signatures of 300 events of the type $\eta$ $\rightarrow$ $\pi^{+}\pi^{-}e^{+}e^{-}$ These data are relevant for tests of the chiral anomaly.

On July 1, the board of directors of the Forschungszentrum Jülich (FZJ) founded the$\textbf{Jülich Center for Hadron Physics (JCHP)}$. The main goal of the JCHP is to coordinatethe hadron physics activities at the FZJ for the FAIR project. This includes activitiesat the Institute for Advanced Simulations (IAS), the Institut für Kernphysik (IKP), theZentralinstitut für Elektronik (ZEL) and the Zentralabteilung Technologie (ZAT). Withinthe Helrnholtz Association (HGF) research field $\textit{Structure of Matter}$, the FZJ operatesthe COSY facility and has achieved an excellent international reputation due to the closecooperation between accelerator physicists, experimentalists and theoreticians. In cooperationwith ZEL and ZAT, the IKP is in charge of the construction and operation of theHigh Energy Storage Ring HESR and makes a strong contribution to the PANDA detectorand its physics. PAX is exploiting methods to effectively polarize (anti-)protons for apossible future upgrade at FAIR.The FZJ operates the JUGENE/JSC supercomputer and hosts the John von Neumann institutewhich develops lattice gauge simulation calculations of quantum chromodynamics(QCD) and hadron structure. The JCHP coordinates these activities by establishing a directconnection between the lattice QCD simulation groups and hadron physicists. Moreover,the infrastructure provided by the IAS for mass storage, presently used for COSYdata, may handle FAIR data and perform Monte Carlo simulations of HESR experiments.External users are essential for the success of an accelerator complex, therefore, the JCHPfacilitates the contact of external users with the FZJ and supports external activities in thefield of hadron physics. Presently an initiative of the universities within North-RhineWestfalia and the FZJ, called NRW-FAIR, is forming to coordinate their FAIR-relatedactivities.Starting December 1, 2008, the IKP-3 theorists also work in IAS-4, the strong interactionphysics branch of the Institute for Advanced Simulations (IAS). The Virtual Institute $\textit{Spinand Strang QCD}$ has presented its first results on June 1 in Ferrara.A Helmholtz-Russia Joint Research Group, the first one in Jülich, will receive fundingfrom the Impuls- und Vernetzungsfond of the Helmholtz Association and from the RussianFoundation for Basic Research for the next three years. In a joint effort of the FZJ,the Budker Institute in Novosibirsk, TU Dortmund and JINR Dubna methods for electroncooling in the MeV region, relevant for FAIR, will be developed.The IKP has initiated a cooperation with the 100-TW laser facility at the HeinrichHeineUniversity Düsseldorf. The potential of new particle acceleration technologies withlimited-mass targets will be explored, exploiting the know-how on frozen-pellet targetsgained at the IKP. The year 2008 has seen important experimental and theoretical progress: [...]