CERN

proton-antiproton collider to search for the intermediate vector bosons 1). The idea was followed up at CERN in the Initial Cooling Experiment ICE. The very encouraging resu1ts 2) led to the approval in July 1978 of a Proton-Antiproton Colliding beam faci1ity3) see also Fig. 1. based on stochastic coo1ing~) which was first proposed by S. van der Meer from CERN. Fi g. 1. Over-a11 site 1ayout. This project has been described in detail previously5)6). Therefore only major features will be reported here, stressing the present performances and showing evidence of the first collisions at Is = 540 GeV observed by the UA1 experiment. STOCHASTIC COOLING The most unusual feature of the ~p complex is the stacking mechanism of the antiprotons in the p accumulator using stochastic cooling. This allows to increase the phase space density of the p-beam in the accumulator by a very large factor