Volume and temperature in αp and αα collisions at very high energy

Two special runs with α particles in the CERN Intersecting Storage Rings allowed the study of collisions of nuclei at the highest accelerator energies. The data obtained simultaneously by five experiments give an impression of the richness of this novel field. Results for elastic αp and αα scattering, for quasi-elastic interactions of nucleons, for hard scattering of constituents of nucleons, and for inelastic interactions are reported. The relevance of interaction volume and temperature is discussed. The modest increase of complexity of their interactions as compared to pp interactions compensates the small size of 4He nuclei. Collisions of ultrarelativistic light nuclei may thus provide a bridge between the well-explored field of high-energy pp collisions and the unexplored field of high-energy nucleus-nucleus collisions. (orig.)