Annual report / Forschungszentrum Jülich Institut für Kernphysik. 1995

Our most prominent experimental result has been announced at the end of the past year: In an international collaboration under the leadership of the IKP production of antihydrogen atoms has been observed at LEAR/CERN for the first time. In Jülich the development of the COSY-accelerator has been continued although at asomewhat slower pace after significant milestones had been passed thus making more beam time available for experiments. The most outstanding achievements were: beam extraction over the full energy range, acceleration of a cooled beam and a tenfold increase of the external beam intensity while simultaneously dramatically reducing the amount of beam halo. The latter development was especially crucial for the data taking of the MOMO collaboration which succeeded in getting the first exclusive data for the pd $\rightarrow$ $^{3}$He $\pi^{+} \pi^{-}$ reaction. The GEM collaboration continued measurements and analysis of pion production in pp reactions. The COSY-TOF collaboration obtained the first measurements of the associated strangeness production pp $\rightarrow$ pK$^{+} \Lambda$ at 2.75 GeV/c. It has more than doubled world's total of such events to date. It could also be shown that multi-particle events in the TOF detector can be measured by high acceptance and completely reconstructed. The first internal target experiment EDDA continued its precision measurements of the elastic pp scattering cross-sections. In the meantime this collaboration collected more than 35 million events over the entire COSY energy range. The improved reconstruction tools of EDDA for the vertices confirmed the high stability of the internal beam in size and position during the acceleration process. The internal cluster target facility COSY-11 has been installed during last spnng. The collaboration, studying the near threshold meson production, observed surprisingly high production probability for $\eta$'-mesons in their first experimental runs. Especially for this experiment a new ion optic of the machine has been developed that strongly raised the luminosity for their measurements. The construction of the 0$^{0}$-facility ANKE has been started [...