Experimental with alpha particles at the CERN intersecting storage rings

Abstract

The successful injection of alpha particles into the CERN Intersecting Storage Rings (ISR) allowed αα and α p interactions to be studied at centre-of-mass (c.m.) energies s = 125 GeV and 88 GeV, respectively, opening up a new energy regime for the investigation of nuclear collisions Five experimental groups took data simultaneously, using detectors which had been developed during 10 years of pp experiments at the ISR. This review begins with an outline of the technical, historical, and physics developments leading to these exceptional runs, followed by a short description of the five detectors which were employed. The results are presented in the order of increasing final-state complexity: elastic scattering quasi-elastic interactions (nuclear breakup without particle production), inelastic processes leading to particle production, and hard (high- p T) interactions. The data are compared with results from pp interactions at corresponding c.m. energies, with extrapolations from nuclear interactions measured at lower energy, and with theoretical expectations and calculations. Whilst it seems that no new phenomena have been uncovered so far, these measurements provide important constraints and guidelines to the search for the predicted new state of matter-the quark-gluon plasma.