Advances in Nuclear Physics – serie

For the first half of the 20th Century, low-energy nuclear physics was one of the dominant foci of all of science. Then accelerators prospered and energies rose, leading to an increase of interest in the GeV regime and beyond. The three articles comprising this end-of-century Advances in Nuclear Physics present a fitting and masterful summary of the energy regimes through which nuclear physics has developed and promises to develop in future. One article describes new information about fundamental symmetries found with kV neutrons. Another reviews our progress in understanding nucleon-nucleus scattering up to 1 GeV. The third analyzes dilepton production as a probe for quark-gluon plasmas generated in relativistic heavy-ion collisions.

The four articles of the present volume address very different topics in nuclear physics and, indeed, encompass experiments at very different kinds of exp- imental facilities. The range of interest of the articles extends from the nature of the substructure of the nucleon and the deuteron to the general properties of the nucleus, including its phase transitions and its rich and unexpected quantal properties. The first article by Fillipone and Ji reviews the present experimental and theoretical situation pertaining to our knowledge of the origin of the spin of the nucleon. Until about 20 years ago the half-integral spin of the neutron and p- ton was regarded as their intrinsic property as Dirac particles which were the basic building blocks of atomic nuclei. Then, with the advent of the Standard Model and of quarks as the basic building blocks, the substructure of the - cleon became the subject of intense interest. Initial nonrelativistic quark m- els assigned the origin of nucleon spin to the fundamental half-integral spin of its three constituent quarks, leaving no room for contributions to the spin from the gluons associated with the interacting quarks or from the orbital angular momentum of either gluons or quarks. That naive understanding was shaken, about fifteen years ago, by experiments involving deep-inelastic scattering of electrons or muons from nucleons.

This volume contains two articles, one providing a historical retrospective of one of the great triumphs of nuclear physics in the 20th century and the other providing a didactic introduction to one of the quantitative tools for understanding strong interactions in the 21st. It is suitable only for advanced graduate courses in nuclear physics.

"Analytic Insights into Intermediate-Energy Hadron-Nucleus Scattering," by R. D. Amado, presents a review of optical diffraction leading into discussions of elastic scattering, single- and multistep inelastic scattering, spin observables, and directions indicated for further research. "Recent Developments in Quasi-Free Nucleon-Nucleon Scattering," by P. Kitching, W. J. McDonald, Th. A. J. Maris, and C. A. Z. Vascon­ cellos, opens with a comprehensive review of the theory, going on to detail frontier research advances in spin dependence in (p, 2p) scattering, isospin dependence, and other quasi-free reactions. The final chapter, "Energetic Particle Emission in Nuclear Reactions" by D. H. Boal, explores new findings regarding direct interactions in the nucleus, thermalization and multiple scattering in nucleon emission, light fragment formation, and production of intermediate-mass fragments. A valuable and instructive trio of papers, Volume 15 of Advances in Nuclear Physics will be of interest to nonspecialists as well as specialists in the fields of nuclear physics, high-energy physics, and theoretical physics.

The reviews in this volume address advances in three important but diverse areas of nuc1ear physics. Within nuc1ear physics it would be hard to provide a wider range of subject matter, style, or treatment. The first artic1e, on quark bags, is a pedagogic artic1e intended to make accessible to the nuc1ear physics community important new ideas from partic1e physics. The second, on interacting boson models, reviews a very interesting and controversial new approach to some of the central problems of nuc1ear spectroscopy. The third, on relativistic heavy-ion physics, is a guide to the extensive literature on a new subject which has been fuH of great expectations, puz- zling data, and speculative ideas. In the past decade, partic1e theorists' understanding of the structure of hadrons has undergone a revolution strikingly similar to that brought about in nuc1ear physics by the introduction of the Iluc1ear sheH model. Like the sheH model, the bag model of hadrons phenomenologically specifies an interior region in which constituents are confined and described by single-partic1e wave functions that are only weakly perturbed by residual interactions.

"Analytic Insights into Intermediate-Energy Hadron-Nucleus Scattering," by R. D. Amado, presents a review of optical diffraction leading into discussions of elastic scattering, single- and multistep inelastic scattering, spin observables, and directions indicated for further research. "Recent Developments in Quasi-Free Nucleon-Nucleon Scattering," by P. Kitching, W. J. McDonald, Th. A. J. Maris, and C. A. Z. Vascon­ cellos, opens with a comprehensive review of the theory, going on to detail frontier research advances in spin dependence in (p, 2p) scattering, isospin dependence, and other quasi-free reactions. The final chapter, "Energetic Particle Emission in Nuclear Reactions" by D. H. Baal, explores new findings regarding direct interactions in the nucleus, thermalization and multiple scattering in nucleon emission, light fragment formation, and production of intermediate-mass fragments. A valuable and instructive trio of papers, Volume 15 of Advances in Nuclear Physics will be of interest to nonspecialists as well as specialists in the fields of nuclear physics, high-energy physics, and theoretical physics. J. W. NEGELE E. VoGT ix CONTENTS Chapter 1 ANALYTIC INSIGHTS INTO INTERMEDIATE-ENERGY HADRON-NUCLEUS SCATTERING R. D. Amado I. Introduction . . . . . . . . . . . . . . . . . . . . .

In both the present volume of Advances in Nuclear Physics and in the next volume, which will follow in a few months' time, we have stretched our normal pattern of reviews by including articles of more major proportions than any we have published before. As a result we have only three review articles in Volume 5. From the beginning of this series it has been our aim, as editors, to achieve variation in the scope, style, and length of individual articles sufficient to match the needs of the individual topic, rather than to restrain authors within rigid limits. It has not been our experience that this flexibility has led to unnecessary exuberance on the part of the authors. We feel that the major articles now entering the series are entirely justified. The article by Professor Delves on "Variational Techniques in the Nuclear Three-Body Problem" is an authoritative, definitive article on a subject which forms a cornerstone of nuclear physics. If we start with two­ body interactions, then the three-nucleon system is, perhaps, the only many­ nucleon system whose exact description may lie within the scope of human ingenuity. In recent years some new techniques of scattering theory, origi­ nating mostly in particle physics, have led to a great deal of new interest in the nuclear three-body problem. In this series we have had two articles (by Mitra and by Duck) on the new approaches.

The three articles of the present volume clearly exhibit a wide scope of articles, which is the aim of this series. The article by Kahana and Baltz lies in the main flow of the large stream of work currently in progress with heavy-ion accelerators. A related article by Terry Fortune on "Multinuclear Transfer Reactions with Heavy Ions" is scheduled to appear in the next volume. The article by Whitehead, Watt, Cole, and Morrison pertains to the nuclear-shell model for which a number of articles have appeared in our series. Our very first volume had an article on how SU(3) techniques can, with great elegance, enable one to cope with the sizable number of states within a configuration. But the actual nuclear force is not exactly that yielded by the elegant techniques, and so interest continued in dealing with the large number of states by brute force. Then the Glasgow school of Whitehead et al. discovered that mathematical techniques existed for coping more simply with the lowest eigenvalues of large matrices. The present ar­ ticle aims generally to make accessible to nuclear physicists the methods developed at Glasgow. The final article by Baer, Crowe, and Truol on radiative pion capture describes a new field of importance because of the advent of the meson factories. More and more pions and muons will become standard tools in nuclear physics.

In the present volume and in the preceding one we have stretched our normal pattern of reviews by including articles of more major proportions than any we have published before. As a consequence each of these two vol­ umes contains only three review articles. From the beginning of this series it has been our aim, as editors, to achieve variation in the scope, style, and length of individual articles sufficient to match the needs of the individual topic, rather than to restrain the authors within rigid limits. We feel that the two major articles of Vols. 5 and 6 are entirely justified and do not repre­ sent unnecessary exuberance on the part of the authors. The article by Michaudon on fission is the first comprehensive account of the developments in this subject, which have placed it in the center of the stage of nuclear physics during the past few years. The discovery of fission isomerism and its dramatic manifestations in the intermediate structure of the neutron cross sections for fissionable isotopes are among the most im­ portant and interesting events to occur in nuclear physics. These events came as a surprise, and reaffirmed that the strength of nuclear physics lies in the combination of ingenious experiments with simple ideas.

The aim of Advances in Nuclear Physics is to provide review papers which chart the field of nuclear physics with some regularity and completeness. We define the field of nuclear physics as that which deals with the structure and behavior of atomic nuclei. Although many good books and reviews on nuclear physics are available, none attempts to provide a coverage which is at the same time continuing and reasonably complete. Many people have felt the need for a new series to fill this gap and this is the ambition of Advances in Nuclear Physics. The articles will be aimed at a wide audience, from research students to active research workers. The selection of topics and their treatment will be varied but the basic viewpoint will be pedagogical. In the past two decades the field of nuclear physics has achieved its own identity, occupying a central position between elementary particle physics on one side and atomic and solid state physics on the other. Nuclear physics is remarkable both by its unity, which it derives from its concise boundaries, and by its amazing diversity, which stems from the multiplicity of experimental approaches and from the complexity of the nucleon-nucleon force. Physicists specializing in one aspect of this strongly unified, yet very complex, field find it imperative to stay well-informed of the other aspects. This provides a strong motivation for a comprehensive series of reviews.

The four articles of the present volume address very different topics in nuclear physics and, indeed, encompass experiments at very different kinds of exp- imental facilities. The range of interest of the articles extends from the nature of the substructure of the nucleon and the deuteron to the general properties of the nucleus, including its phase transitions and its rich and unexpected quantal properties. The first article by Fillipone and Ji reviews the present experimental and theoretical situation pertaining to our knowledge of the origin of the spin of the nucleon. Until about 20 years ago the half-integral spin of the neutron and p- ton was regarded as their intrinsic property as Dirac particles which were the basic building blocks of atomic nuclei. Then, with the advent of the Standard Model and of quarks as the basic building blocks, the substructure of the - cleon became the subject of intense interest. Initial nonrelativistic quark m- els assigned the origin of nucleon spin to the fundamental half-integral spin of its three constituent quarks, leaving no room for contributions to the spin from the gluons associated with the interacting quarks or from the orbital angular momentum of either gluons or quarks. That naive understanding was shaken, about fifteen years ago, by experiments involving deep-inelastic scattering of electrons or muons from nucleons.

Review articles on three topics of considerable current interest make up the present volume. The first, on A-hypernuclei, was solicited by the editors in order to provide nuclear physicists with a general description of the most recent developments in a field which this audience has largely neglected or, perhaps, viewed as a novelty in which a bizarre nuclear system gave some information about the lambda-nuclear intersection. That view was never valid. The very recent developments reviewed here-particularly those pertaining to hypernuclear excitations and the strangeness exchange reactions-emphasize that this field provides important information about the models and central ideas of nuclear physics. The off-shell behavior of the nucleon-nucleon interaction is a topic which was at first received with some embarrassment, abuse, and neglect, but it has recently gained proper attention in many nuclear problems. Interest was first focused on it in nuclear many-body theory, but it threatened nuclear physicists'comfortable feeling about nonrelativistic potential theory, and many no doubt hoped that it would remain merely an esoteric diversion within the many-body cult. In the editors' opinion, this subject is now emi­ nently respectable and a review of it indeed timely. The third topic, nuclear charge distributions, is one which almost every nuclear physicist believed had been weIl in hand for some years.

The present volume reaffirms nuclear physics as an experimental science since the authors are primarily experimentalists and since the treatment of the topics might be said to be "experimental." (This is no reflection on the theoretical competence of any of the authors.) The subject of high-spin phenomena in heavy nuclei has grown much beyond the idea of "backbending" which gave such an impetus to its study five years ago. It is a rich, new field to which Lieder and Ryde have contributed greatly. The article "Valence and Doorway Mechanisms in Resonance Neutron Capture" is, in contradistinction, an article pertaining to one of the oldest branches of nuclear physics-and it brings back one of our previous authors. The Doppler-shift method, reviewed by Alexander and Forster, is one of the important new experimental techniques that emerged in the previous decade. This review is intended, deliberately, to describe thoroughly a classic technique whose elegance epitomizes much of the fascination which nuclear physics techniques have held for a generation of scientists. This volume concludes the work on the Advances in Nuclear Physics series of one of the editors (M. Baranger), whose judgment and style characterize that which is best in the first ten volumes. Many of our readers and most of our authors will be grateful for the high standards which marked his contributions and which often elicited extra labor from the many authors of the series.

This volume contains two major articles, one providing a historical retrosp- tive of one of the great triumphs of nuclear physics in the twentieth century and the other providing a didactic introduction to one of the quantitative tools for understanding strong interactions in the twenty-first century. The article by Igal Talmi on “Fifty Years of the Shell Model – the Quest for the Effective Interaction”, pertains to a model that has dominated nuclear physics since its infancy and that developed with astonishing results over the next five decades. Talmi is uniquely positioned to trace the history of the Shell Model. He was active in developing the ideas at the shell model’s inception, he has been central in most of the subsequent initiatives which expanded, cl- ified and applied the shell model and he has remained active in the field to the present time. Wisely, he has chosen to restrict his review to the domin- ing issue: the choice of the effective interactions among valence nucleons that determine the properties of low lying nuclear energy levels. The treatment of the subject is both bold and novel for our series. The ideas pertaining to the effective interaction for the shell model are elucidated in a historical sequence.

For the first half of the 20th Century, low-energy nuclear physics was one of the dominant foci of all of science. Then accelerators prospered and energies rose, leading to an increase of interest in the GeV regime and beyond. The three articles comprising this end-of-century Advances in Nuclear Physics present a fitting and masterful summary of the energy regimes through which nuclear physics has developed and promises to develop in future. One article describes new information about fundamental symmetries found with kV neutrons. Another reviews our progress in understanding nucleon-nucleus scattering up to 1 GeV. The third analyzes dilepton production as a probe for quark-gluon plasmas generated in relativistic heavy-ion collisions.