The target area of the external COSY experiments

For hadron physics experiments the combination of a well defined cooled particle beam and a small target volume provides a well defined interaction vertex. With a thin target a precise energy definition is obtained and systematic errors due to Coulomb scattering and secondary interactions with the target material are reduced. A liquid hydrogen/deuterium target of a few millimeter length has been constructed and operated since three years in the external experiments at COSY Juelich. A small target together with a wide acceptance of the detectors behind require the diminution of background reactions. Therefore, very thin target windows of 0.9 μm Mylar foils are realized with the use of a purely mechanical pressure stabilization system. With a fast heating system one can overcome the problem of background reactions with rest gas condensing on the foils. For the precise definition of the incoming beam, veto systems consisting of two annular plastic scintillators are installed before the target in order to detect all particles not passing through the target cell and their reaction products. The improvements of the liquid hydrogen/deuterium target and the design of veto systems are described. (orig.)