This Workshop was organized to bring once more tagether the scientists of the rather heterogeneaus field of exotic atoms. At present the main topic of the field seems to be the study of the atomic cascade. There are some who study it intentionally -Iet us call them cascadeurs -and others who think they investigate other features of the exotic atoms (like Coulomb capture, particle transfer, muon catalyzed fusion, chemical effects, fundamental properties, etc.) -users-while in fact they study some special consequences of the same atomic cascade. We decided to get cascadeurs and users discuss the problems of exotic atoms at wonderful Erice, at the 5th Course of the International School of Physics of Exotic Atoms. Our Workshop was quite successful, we have heard excellent talks from participants from a dozen countfies and most of them have prepared written contributions for this volume. The Organizers express their gratitude to all participants for their contributions, especially to David Measday for bis concluding remarks (not printed here) and to James Cohen for jumping in for Leonid Ponomarev who had to leave unexpectedly in the middle of the meeting. We greatly appreciate the enthusiastic help of Marianne Signer in every stage of the organization work. Am , of course, the Workshop could not happen at all without the incredibly efficient organization by the Ettore Majorana Centre of Scientific Culture. Leopold M. Simons Dezso Horvath Gabriele Torelli V CONTENTS OPENING ADDRESS . . . . . . . . . . . . . . . . . . . . . . . . . . xi . . . . . . ."

This Workshop was organized to bring once more tagether the scientists of the rather heterogeneaus field of exotic atoms. At present the main topic of the field seems to be the study of the atomic cascade. There are some who study it intentionally -Iet us call them cascadeurs -and others who think they investigate other features of the exotic atoms (like Coulomb capture, particle transfer, muon catalyzed fusion, chemical effects, fundamental properties, etc.) -users-while in fact they study some special consequences of the same atomic cascade. We decided to get cascadeurs and users discuss the problems of exotic atoms at wonderful Erice, at the 5th Course of the International School of Physics of Exotic Atoms. Our Workshop was quite successful, we have heard excellent talks from participants from a dozen countfies and most of them have prepared written contributions for this volume. The Organizers express their gratitude to all participants for their contributions, especially to David Measday for bis concluding remarks (not printed here) and to James Cohen for jumping in for Leonid Ponomarev who had to leave unexpectedly in the middle of the meeting. We greatly appreciate the enthusiastic help of Marianne Signer in every stage of the organization work. Am , of course, the Workshop could not happen at all without the incredibly efficient organization by the Ettore Majorana Centre of Scientific Culture. Leopold M. Simons Dezso Horvath Gabriele Torelli V CONTENTS OPENING ADDRESS . . . . . . . . . . . . . . . . . . . . . . . . . . xi . . . . . . ."

The fourth course of the International School of Physics of Exotic Atoms took place at the "Ettore Majorana" Center for Scien tific Culture, Erice, from March 31 to April 6, 1984. As tradition, exotic atoms have been a tool for studying elec tromagnetic, weak and strong interactions at low energies. We felt it appropriate to have a full course devoted to a discussion of the information to be gained on the fundamental interactions from the study of low energy systems. In this kind of physics, which is characterized experimentally by very intense particle sources and very sensitive apparatuses, one can search for rare events and can perform precise measurements. Sensitive tests of the predictions of current theories of electro weak and strong interactions can thus be achieved. The course was attended by 54 participants from 23 institutes in 9 countries. The morning lectures reviewed the achievements of the field in the last few years and the afternoon seminars dealt with new results and projects."

A fundamental step towards gaining a deeper understanding of our world is to increase the resolution of the investigative instruments we use; i.e. to increase the energy, and hence to decrease the wavelength, of the particles which constitute our probes. Almost any substantial progress in our understanding of the fundamental laws of Nature has been obtained when a new generation of accelerators has allowed us to achieve a new energy range. The new results have generated new questions, thus encouraging us to construct new machines to reach even higher energy levels. The relative energy gain from one generation of accelerators to the next is progressively increasing. The energy ga in suggested by the theoretical predictions at the time has usually been much greater than the value allowed by our technical capabilities. But this smaller energy gain permitted by accelerator technology improvement has generally been sufficient up until now to bring about a substantial increase in our knowledge. Hence a large increase in accelerator energy is very important, and we know that this result can essentially be obtained by developing some new device or some new approach.