Nuclear PhysicsA482 (1988) 313c-328c 313c North-Holland, Amsterdam ELECTROMAGNETIC EXCITATION OF ONE- AND MULTIPHONON GIANT RESONANCE STATES WITH RELATIVISTIC HEAVY IONS Gerhard BAURand Carlos A. BERTULANI* Institut fur Kernphysik, Kernforschungsanlage JUlich GmbH, Postfach 1913, 5170 JUlich, F.R.G. 1. INTRODUCTION Relativistic Heavy Ion (RHI) accelerators exist already in some places of the world, and more of them are being built or planned. There is the BEVALAC (~ 1-2 GEV/A), Brookhaven (~ 15 GEV/A) and CERN (60 and 200 GEV/A). In Darm- stadt, SIS/ESR will be built and a relativistic heavy ion collider, RHIC, is planned in the USA.The strong motivation for the investigation of RHI colli- sions is the study of nuclear matter under extreme conditions, of special interest is the study of the theoretically expected quark-gluon-plasma phase. RHI's provide a unique opportunity. It is the aim of the present paper to show that, in addition to the central nuclear collisions, the distant collisions (see Fig,l) are also interesting. It is the extremely short and strong pulse of electromagnetic radiation which leads to new effects. The investigation of electromagnetic properties of nuclei with Coulomb excitation at non-relativistic and sub-barrier energies and with electrons (A1-66, A1-75) is a very fruitful tool. The various probes complement each other in the study of electromagnetic properties. In non-rel- ativistic Coulomb excitation one can ideally investigate low lying collective states, with heavy ions multiple excitation can be very strong. On the other hand, electron scattering can be well described by a one-photon exchange mechanism. Since the electrons do not interact strongly, they can penetrate the nucleus easily, and form-factors can be determined as a function of the three-momentum transfer ~ and excitation energy m . Due to the condition that strongly interacting projectiles should not penetrate through each other in the Coulomb excitation process, one can only obtain information about the electromagnetic matrix-elements at the "photon point" (I~I = ~) in this case. Apart from the interest in electromagnetic processes for their own sake, they can also be of more practical importance. E.g. the copious production of + - e e pairs in RHI collisions can serve to keep control of the beam luminosity in a RHI collider (An-87). On the other hand, it is also important to under- *present and permanent address: Federal University of Rio de daneiro, Brazil 0375-9474/88/$03.50 © Elsevier Science Publishers B.V, (North-Holland Physics Publishing Division)