Research Reports in Physics

Research Reports in Physics

Nuclear Structure of the Zirconium Region Editors: 1. Eberth, R. A. Meyer, and K. Sistemich

Ecodynamics Contributions to Theoretical Ecology Editors: W. Wolff, C.-l. Soeder, and F. R. Drepper

Nonlinear Waves 1 Dynamics and Evolution Editors: A. V. Gaponov-Grekhov, M. I. Rabinovich, and 1. Engelbrecht

Nonlinear Waves 2 Dynamics and Evolution Editors: A. V. Gaponov-Grekhov, M. I. Rabinovich, and 1. Engelbrecht

Nonlinear Waves 3 Physics and Astrophysics Editors: A. V. Gaponov-Grekhov, M. I. Rabinovich, and 1. Engelbrecht

Nuclear Astrophysics Editors: M. Lozano, M. I. Gallardo, and 1. M. Arias

Optimized LCAO Method and the Electronic Structure of Extended Systems By H. Eschrig

Nonlinear Waves in Active Media Editor: J. Engelbrecht

Problems of Modern Quantum Field Theory Editors: A. A. Belavin, A. U. Klimyk, and A. B. Zamolodchikov

Fluctuational Superconductivity of Magnetic Systems By M. A. Savchenko and A. V. Stefanovich

Nonlinear Evolution Equations and Dynamical Systems Editors: S. Carillo and O. Ragnisco

Nonlinear Physics Editors: Gu Chaohao, Li Yishen, and Tu Guizhang

Nonlinear Waves in Waveguides with Stratification By S. B. Leble

Quark-Gluon Plasma Editors: B. Sinha, S. Pal, and S. Raha

Symmetries and Singularity Strnctures Integrability and Chaos in Nonlinear Dynamical Systems Editors: M. Lakshmanan and M. Daniel

Modeling Air-Lake Interaction Physical Background Editor: S. S. Zilitinkevich

Nonlinear Evolution Equations and Dynamical Systems NEEDS '90 Editors: V. G. Makhankov and O. K. Pashaev

Solitons and Chaos Editors: I. Antoniou and J. F. Lambert

Electron-Electron Correlation Effects in Low-Dimensional Conductors and Superconductors Editors: A.A. Ovchinnikov and 1.1. Ukrainskii

Signal Transduction in Photoreceptor Cells Editors: P.A. Hargrave, K. P. Hofmann, and U. B. Kaupp

Nuclear Physics at the Borderlines Editors: J. M. Arias, M.I. Gallardo, M. Lozano

1.M. Arias M.I. Gallardo M. Lozano (Eds.)

Nuclear Physics at the Borderlines Proceedings of the Fourth International Summer School, Sponsored by the Universidad Hispano-Americana, Santa Marfa de la Rabida, La Rabida, Huelva, Spain, June 17-29, 1991

With 92 Figures

Springer-Verlag Berlin Heidelberg New York London Paris Tokyo Hong Kong Barcelona Budapest

Dr. Jose Miguel Arias Dr. Maria Isabel Gallardo Professor Dr. Manuel Lozano Dept. Ffsica Atomica, Molecular y Nuclear, Facultad de Ffsica, Universidad de Sevilla, Apdo. 1065,41080 Sevilla, Spain

ISBN-13:978-3-540-55074-7 DOT: 10.1007/978-3-642-84708-0

e-ISBN -13 :978-3-642-84 708-0

This work is subject to copyright. All rights are reserved. whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations. recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is per­mitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law.

© Springer-Verlag Berlin Heidelberg 1992

The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regula­tions and therefore free for general use.

Typesetting: Camera ready by authors

57/3140-543210- Printed on acid-free paper

Preface

This volume contains the lectures presented by invited speakers at the IV La Rlibida International Summer School on Nuclear Physics. This was the IV edition of a summer school organized by our group every three years on topics related to nuclear physics. This Summer School was aimed mainly at young nuclear physicists, both theoreticians and experimentalists, engaged in research work at predoctoral or recent postdoctoral level.

The topics treated in the three previous editions of the School were: "Heavy Ion Collisions", "Theory of Nuclear Structure and Reactions" and "Nuclear As­trophysics". This year's School was entitled "Nuclear Physics at the Borderlines". Special emphasis was placed on those topics along which nuclear physics is ex­pected to develop in the next few years. The aim of the School was to provide the attendants with an opportunity to get into close contact with experienced researchers and listen to their account of the present state-of-the-art in nuclear physics and the main future lines of development.

We would like to express our appreciation to all the lecturers who kindly accepted our invitation to give a talk at the IV La Rlibida International Summer School on Nuclear Physics at the Borderlines. They made an important effort and succeeded in presenting their talks in a pedagogical way at the School itself as well as in the written version presented in this volume. Their presence during the School facilitated many informal scientific discussions during the beach and bar "sessions" and contributed to the excellent atmosphere among all the participants.

The organization found a main sponsor in the Universidad Hispano-Americana Santa Marla de La Rabida, which provided important financial support. The School was held in its buildings and we are most grateful to the entire staff. Considerable financial support was provided also by the Spanish government through the Direcci6n General de Investigaci6n Cientffica y Tecnica (DGICyT) and by the regional government through the Consejeria de Educaci6n de la Junta de Andalucfa. We also received financial assistance from the following banks: Banco Espanol de Credito and Caja de Ahorros y Monte de Piedad de Huelva y Sevilla. We express our deep gratitude to all of them.

VI

Special thanks are given to the participants from the Departamento de Ffsica At6mica, Molecular y Nuclear at Seville University for their enthusiastic coop­eration before, during and after the School. Our gratitude to Elena Arbella and Jose Di'az for their continuous assistance in the organiztion of the School.

Sevilla, Spain September, 1991

.l.M. Arias M.l. Gallardo

M. Lozano

Contents

Dispersion Relation Approach to the Nuclear Mean Field

By C. Mahaux and R. Sartor

Nuclear Collective Motion

By D.M. Brink

Heavy-Ion Interactions at Intermediate Energies

By A. Vitturi, S.M. Lenzi and F. Zardi

New Physics Far From Stability

By A. Poves

Recent Developments in High Spin Physics

By J .L. Egido

Recent Spectroscopy of Exotic Nuclear Shapes at High Spin

By M.A. Bentley

Nuclear Phase Transitions at Finite Temperature

By A.L. Goodman

Algebraic Approach to Molecular Spectra

By A. Frank

Algebraic Model of Hadronic Structure

By F. Iachello

1

15

31

45

51

70

94

111

130

VIII

Ultrarelativistic Heavy-Ion Collisions: Present and Future

By G. Baym

Electron Scattering

By I. Sick

The Role of Coloured Quarks and Gluons in Hadrons and Nuclei

By F.E. Close

Quarks in Nuclei

By A. Ferrando, P. Gonzalez and V. Vento

Chiral Models of Low Energy QCD

By G. Ripka

Random-Matrix Modelling of Stochastic Nuclear Properties

By H.A. Weidenmiiller

Subject Index

List of Participants

155

172

194

212

233

255

261

263

Introduction

J.M. Arias, M. Gallardo and M. Lozano

Departamento de Fisica At6mica, Molecular y Nuclear

Facultad de Fisica, Universidad de Sevilla

Apdo. 1065. 41080 Sevilla, Spain

This volume contains the lectures presented by the invited speakers at the IV La

Rabida International Summer School on Nuclear Physics. It was held in La Rabida

(Huelva), Spain from June 17th to 29th, 1991.

The title of this edition of the School was Nuclear Physics at the Borderlines. Spe­

cial emphasis was devoted to topics along which presumably most nuclear physicists will

look into in the next few years. The title was obviously too ambitious. It was certainly

impossible to cover in one School all branches of nuclear physics and its connections

with other fields. We chose some topics that are indeed borderlines, but unfortunately

many others (as important as astrophysics or material analysis) had to be left out.

When selecting the topics to be presented at La Rabida School, we decided to

consider two basic ways of approaching the borderlines of nuclear physics. One of

them is through the new and more accurate data available due to the development of

experimental techniques. The other is provided by the application of theoretical models

or techniques borrowed from other fields or, reciprocally, the application of the models

and techniques developed in nuclear physics in different scientific areas.

In the first group we include the study of high spin, temperature and exotic nuclear

phenomena which are being measured due to more sensitive detector arrays. Lectures

by Profs. M.A. Bentley, J .L. Egido and A.L. Goodman dealt with this topic.

- The development of large arrays of high resolution low signal-to-noise "I-ray detec­

tors has allowed the observation of weakly populated exotic structures in nuclei, as

those related to nuclear superdeformed shapes. Prof. Bentley presented this topic

and also included a discussion on future developments in "I-ray detector arrays as

EUROGAM and GAMMASPHERE.

The theoretical treatment used to study high spin in nuclear physics was discussed by

Profs. Goodman and Egido.

- Prof. Goodman's lectures were devoted to study temperature effects. He uses the

language of statistical mechanics applied to small systems and studies the way that

transitions in some collective order parameters (shape transition, ~ transition, etc.)

are induced by temperature.

- Prof. Egido presents the study of new phenomena related to octupole nuclear

shapes and superdeformation. The rotational damping produced at moderate tem-

x

peratures is also discussed in his lectures. Theories beyond the mean field approach

are used to calculate microscopically the strength function of hot rotating nuclei.

Also in this first group we include the study of the structure of the traditional "elemen­

tary" particles in nuclear physics (nucleons) revealed in experiments exploring nuclear

collisions at higher energy. The lectures by Profs. G. Baym, F.E. Close, G. Ripka, I.

Sick and V. Vento treats this topic from different points of view.

- Prof. Baym presents a detailed discussion of the program on ultrarelativistic heavy­

ion collisions underway at CERN and Brookhaven National Laboratory. He ana­

lyzes how new physical phenomena produced by fundamental interactions can be

found in those systems. An example is the production of a new state of matter:

the quark-gluon plasma.

- Prof. Vento starts giving a short review of some properties of Quantum Chromody­

namics (QCD) and then introduces low energy models of hadron structure. Those

models are applied to exotic nuclei, quark matter, deep inelastic scattering, etc.

- The complexity of "deriving" nuclear structure from QCD is emphasised in Prof.

Close's lectures. He presents a comparison between QED-molecular forces and

QCD-nuclear forces, where only colour confinement breaks the analogy. Applica­

tions of colour degree of freedom, Pauli's principle and spin-flavour correlations are

discussed in his lectures, in particular the magnetic moment of hadrons and proton

spin.

- Electron scattering has been shown to be one of the most efficient tools to study

hadron structure and there are important programs of development underway such

as CEBAF. This field is covered in Prof. Sick's lectures. He presents the topic and

then concentrates on two special cases: the study of charge distributions in the lead

region and the determination of neutron form factors.

- Prof. Ripka presents two possible descriptions of a nuclear process: using either nu­

cleons or quarks as intermediate fermions. He discusses the possibility of obtaining

the same answer with both treatments. Two processes related to the propagation of

hadrons in a dense baryonic medium are presented: the polarization of the medium

and the change in the hadron's quark structure. The last part of Prof. Ripka's

lectures is devoted to the relation between the scaling of effective lagrangians and

the changes in the quark constituent masses.

Finally in this first group, the use of radioactive beams and the improvement of detection

techniques have allowed to extend the nuclear domain to very neutron rich nuclei far

from the line of {3 stability.

- This is the topic discussed by Prof. A. Poves in his lectures.

XI

In the second group we include the following lectures.

- Prof. D.M. Brink deals with the finite size effects in nuclei and other quantum sys­

tems (particle physics, condensed matter physics, astrophysics, ... ). He presents

a detailed discussion of these effects in relation with the quark-gluon plasma

(droplets), the pairing phase transitions in nuclei, two nucleon transfer reactions

and superdeformation.

- Prof. A. Vitturi uses Glauber-type models to describe nuclear grazing collisions at

intermediate energies, E/ A ~ 50 - 1000 MeV/A. It is shown in his lectures that

this model can be used to determine microscopic heavy-ion optical potentials in this

energy range. The treatment of both elastic and inelastic scattering is presented.

The power of group theory is well known in physics. In particular, it has been very

successful in connection with models of nuclear structure. The application of similar

techniques to systems of lower (molecular) and higher (hadronic) energies was presented

at the School.

- In his lectures, Prof. A. Frank shows how to apply group theoretical technology to

the description of molecular physics. He studies molecular excitations, described in

terms of products of U(2) and U(4) groups and presents a unified way of treating

vibrational, rotational and electronic excitations in diatomic molecules.

- Prof. F. Iachello introduces the use of group theoretical techniques to the study

of hadron structure. The algebraic model of hadron structure exploits the algebra

U(4) ® SU.(2) ® SU f(n) ® SUc (3). The different groups correspond to orbital,

spin, flavour and colour, respectively. The model can accomodate previous results

and describe new possibilities.

Also in this set of topics, we include the description of chaos and its application to

nuclear physics problems. This was the content of the lectures presented by Profs. H.A.

Weidenmuller and O. Bohigas.

- Prof. Weidenmuller discusses the use of random matrices and its applications to

nuclear physics and other fields.

- Prof. Bohigas introduces the treatment of the chaotic dynamics and its relation

with quantum systems.

Finally, there are still very interesting problems in "traditional" nuclear physics.

One of them, the use of mean field techniques, was treated by Professor C. Mahaux in

his lectures.

- Prof. Mahaux studies the mean field theory for systems with both positive and

negative energies. An imaginary part describes the coupling between single-particle

and more complicated degrees of freedom. Real and imaginary parts are linked

by dispersion relations which allows an extrapolation of the mean field towards

negative energies.

XII

We feel that, although certainly incomplete, many of the important borderlines of

nuclear physics were discussed in the School and that the interested reader will find

in this volume a useful overview of the current situation in this field. In addition, the

lectures are written in a pedagogical way so as to allow the reader to understand the

main ideas behind these exciting research areas.