Operation of the P ¯ ANDA cluster-jet target with the HESR stochastic cooling at COSY

The P ¯ ANDA experiment at the High Energy Storage Ring (HESR) of the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, will be a unique setup to study the strong interaction in antiproton-proton collisions. The combination of a windowless cluster-jet target and a high-intensity antiproton beam, cooled by stochastic cooling down to momentum spreads of 4 × 10 − 5 in the presence of the target, is ideal to study, e.g., the line shape of exotic candidates in the charmonium spectrum, such as the χ c 1 ( 3872 ) . For first studies on the performance of the cluster-jet target and the stochastic cooling, both were installed at the COoler SYnchrotron (COSY) at the Forschungszentrum Jülich, Germany. Detailed studies on the beam quality for different target settings with different densities were performed and will be presented in this paper. The results show that the cluster-jet target is able to provide the required hydrogen target thickness of more than 2 × 10 15 atoms / cm 2 for the P ¯ ANDA experiment and that the stochastic cooling is able to efficiently cool the beam in presence of such a target thickness, although the system is not yet complete compared to the setup foreseen for the HESR. The presented results strengthen the theoretical understanding of the beam-target interaction and stochastic cooling performance and will provide important input for operation later at the HESR.