V. IMPLICATIONS OF SCIENTIFIC

OPPORTUNITIES

Many important and challenging scientific opportunities are confronting our field, as is apparent from the Scientific Questions posed in Chapter II. We here wish to present the major implications of these opportunities in terms of resources.

Recognition of some of the simplicity and symmetries underlying nuclear structure has enabled us to begin to work toward a new level of correlation of nuclear data and an understanding of the microscopic origins of that structure. The discovery of entirely new structural phenomena such as the observation of spin-flip giant resonances, have been matched by the observation of entirely new reaction mechanisms, such as deep inelastic scattering, that are not yet fully understood. New classes of accelerators are beginning to permit study of the structure of the nuclear continuum and of how the nuclear many-body system responds to increasing energy and angular momentum. Whole new parameter ranges are being opened for the first time to precision study.

There are interesting and vita! open questions in nuclear physics that require investigation and understanding in nuclear structure and in the dynamics of nuclear interactions that hitherto were inaccessible. We will be able to address these now or in the near future with new or newly upgraded facilities, or ones that are presently under construction. These provide advanced new capabilities for the study of electromagnetic interactions at energies below 1 GeV, of nucleus-nucleus collisions with improved capabilities in the regime of normal nuclear dynamics and in the transition region around the nuclear "sonic barrier," and of light-ion reactions using the high resolution capabilities of stored and cooled beams. Exploitation of these capabilities holds great promise for scientific advances in the near term.

A new theme in nuclear physics that emerges in this report concerns the implications of QCD, the fundamen

tal framework for our characterization of the strong interaction, in the nuclear many body system. This theme shines through a number of the topics that are discussed in Chapter II. In particular, the 4-GeV electron accelerator recently endorsed by NSAC is an important tool to address these questions. Both in this field and in the domain of electroweak interactions, traditional dividing lines between nuclear physics and particle physics are shifting. This is certainly healthy; the divisions are perhaps somewhat historical and sociological in origin, but there are also real, important differences in intellectual perspectives, particularly in the appreciation by nuclear physicists of the importance of many-body dynamics and the real possibilities that collective phenomena contain new physics and qualitatively new insights into the fundamental nature of matter.

The facilities and instrumentation needed to confront a variety of important opportunities in the future are discussed below by classifying them according to the types of particle beams.

Relativistic Heavy Ion Collider

In this Long Range Plan, we identify the scientific opportunities presented by an accelerator that can provide colliding beams of very heavy ions at about 30 GeV per nucleon and recommend that it be the next major construction project for nuclear science.

Having made the above recommendation, we note that this will be a project of unusual magnitude for our field. Both the accelerator ideas and the underlying physics concepts of this recommendation were pioneered in the United States. Considerably more R&D will have to be expended, both prior to formal proposals and during the construction phase of the accelerator. Although the design of the accelerator is within the framework of existing technology, many problems and alternative solutions will have to be studied. Various possible ion sources. techniques of injection and acceleration of the heavy ion

beams, and the design of the appropriate magnet structures are among the features that need attention.

The detector problems will be formidable. Although multiplicities (the number of particles produced in a single collision, that will have to be detected simultaneously) will, in general, be substantially higher than in nucleonnucleon collisions at very high energies, the requirements on spatial resolution of detectors, or granularity, may not be much greater. Important physics may be signalled by the number of strange particles relative to ordinary hadrons, by di-lepton pairs, or simply by the flow pattern in the thousands of reaction products. Detector systems for all these experiments will have to be thought out, designed and built with the same amount of care as the main facility. Since the scale of these detectors will be comparable to those used in high energy physics, that experience will have to be used as a basis of further R&D efforts.

The only present facility for research with relativistic heavy ions in the U.S. is the Bevalac, and with the variety of beams and energies available, it is a unique facility anywhere. Some beams at higher energies will probably be available sporadically at CERN over the next few years. In order to begin to understand the problems associated with the physics of the future colliding beam accelerator, it would be desirable to carry out experiments in the U.S. with heavy ions at energies significantly higher than those of the Bevalac. Such measurements would provide needed data concerning nuclear stopping power, particle multiplicities and detector technology. Exploratory experiments at energies that will begin to test our ideas about nuclear compressibility and attainable nuclear den. sities can attract the new generation of scientists, as wel! as provide the experience that will be essential to the development of the physics program over the next decade at this new collider facility.

In the preconstruction phase it is especially important that NSAC and suitable workshops and subcommittees be charged with giving advice periodically on the best course for the physics program, accelerator characteristics, and detector needs associated with this major scientific endeavor. Since this is a border area, of close interest to high energy physicists, some attention should be given to including leading members of that community in the process of helping specify the course of this new undertaking. Pions, Kaons, Muons, Neutrinos, and Antiprotons

The pion capabilities of LAMPF are being utilized in a strong program of experimental studies. The use of pions in nuclear structure physics, exploiting their sharp spinisospin selectivity in the delta region, is an outstanding

and unique opportunity. There is a possibility for enhancing our present capabilities through a new pion channel, allowing access to higher energy pions as well as improved resolution, counting rate, and possibly duty factor. Such a new pion beam should be coupled to a new high resolution pion spectrometer. The characterization and understanding of the behavior of the delta (the simplest nonnucleonic excitation) in the nucleus is an important element in much of hadronic nuclear physics. A large solid-angle multiparticle spectrometer may be important for this work.

The electroweak theory of Glashow, Salam, and Weinberg has had spectacular confirmation with the discovery of the intermediate vector bosons, the W* and Z° at CERN. This theory and QCD constitute the Standard Model which forms the basis of nuclear interactions. Numerous opportunities exist for probing the validity of this model. Improved kaon beams can be used to search for decays and other processes not present in the Minimal Standard Model. Better neutrino beams coupled with high granularity, high mass, tracking detectors can search for new interactions beyond those of the standard model, and for neutrino oscillations. Muon beams with improved duty factor can be used, for instance, to search for muon number nonconserving processes. Neutrino-nucleus scattering could further probe the structure of the weak neutral current. Such reactions also provide a tool to probe new aspects of nuclear structure.

Improved kaon facilities could provide much better counting rate and better resolution for important studies of hypernuclei. Higher energy kaon beams and spectrometers would allow searches for the as yet unobserved doubly strange states of hypernuclei. These same facilities would make possible the use of kaons for inelastic scattering and for studies of strange resonances in nuclear

matter.

Antiprotons can provide a unique tool for probing the foundations of the strong interaction, for studying possible exotic quark configurations, and for producing a very hot small region within nuclear matter. A new source appears to be beyond the resources of our community. However, an antiproton storage ring, or possibly a new time separated antiproton beam, at an existing facility may provide a unique opportunity for cost-effective experimentation with antiprotons.

A major new "Kaon Factory," a 10-30 GeV proton accelerator with 1014-1015 protons per second, would provide substantial opportunities for physics in all of these areas. This physics is clearly very fundamental, important, and exciting. Given our commitment to the construction of the National Electron Accelerator Laboratory and the

heavy ion collider discussed above, the financial assumptions of this report preclude a major additional facility. But as circumstances change, we want to keep this important option readily available: it clearly presents many unique opportunities.

In the meantime we have many opportunities for physics which can be done without such a major new accelerator. Among these opportunities are new experiments on solar neutrinos, experiments on nuclear beta decay and double beta decay, and opportunities to take advantage of new kaon beams, new muon facilities, new neutrino beams and detectors, and new pion beams and spectrometers at existing accelerators.

Electromagnetic Facilities

It is clear that electromagnetic probes will play an increasingly important role in many areas of nuclear physics. Questions about the nucleon-nucleon interaction, about connections to QCD and the quark structure, about the hadronic structure of nuclei, elementary excitations and nuclear-structure symmetries, all require electromagnetic probes. The new 4 GeV electron facility at NEAL is clearly the major near-term new initiative in nuclear physics. Its completion is awaited eagerly by our community. The cost of this accelerator and that of its first generation of experimental facilities was discussed and estimated in the report of the NSAC Panel on Electron Facilities, which also noted that a strong scientific case can be made for CW electron capability with high resolution below 1 GeV. We see such a lower-energy capability as a major opportunity for the field in studies on the deuteron, on hadronic degrees of freedom, particularly in the delta regime, on many aspects of the elementary excitations and structural symmetries of nuclei and, with longitudinally polarized electron beams, on the structure of semileptonic neutral weak currents.

Light Ion Facilities

Light ions are the oldest probes of nuclear structure. Yet as the scientific questions show, refinement of these probes has yielded qualitatively new discoveries of fundamental importance, and holds great promise for the future. Scientific opportunities call for the upgrade of existing facilities to yield variable energy protons in the energy range from 200-500 MeV, polarized protons in this region and below with substantially improved intensity and reasonably intense polarized proton beams at variable energies up to several GeV. They also call for secondary polarized neutron beams of useful intensities with energies to at least 200 MeV (up to perhaps 60 MeV this can be accomplished with upgrades of existing facilities, but the higher energy neutrons may require a new facility).

Heavy lon Facilities

With energies below 200 MeV per nucleon, the facilities that exist or are under construction have many of the features that are required to study the key scientific problems in the area. The completion of the National Superconducting Cyclotron Laboratory and of ATLAS will be major innovative technical achievements and provide important new capabilities. One still needed is the ability to obtain very heavy (up to uranium) beams of variable energy between 3 and 20 MeV per nucleon, a capability that is important in nuclear structure studies, and that could become critically important if present indications of long-lived nuclear molecules in very heavy systems are confirmed. There are needs for larger detector systems in heavy-ion physics, in arrays of photon detectors and in large area systems for charged particles, all requiring adequate data handling systems.

Manpower

The importance of having sufficient skilled and innovative scientists is evident, especially in view of the new initiatives considered here. This is not an issue readily amenable to administrative action. In Sec. IV.1 we iden tified a number of measures that should be taken to assure adequate training of new manpower, though the intellectual vitality of the problems facing us is likely to be the most important advantage in attracting a new generation of physicists.

The support for nuclear theorists has increased since the last Long Range Plan from 5 to 6% of the total nuclear physics budgets. This is a necessary trend, since much of the physics confronting us requires careful prior theoretical thought and substantial theoretical interpretation of the results. We recommend that this trend be continued.

International collaborations are becoming of increasing importance to nuclear physics around the world, and we are pleased that the funding agencies are doing their best to facilitate these. An important issue is the ease with which foreign travel can be arranged, both for U.S. scientists abroad and for arranging visits by foreign scientists in the U.S. The easy interchange of people and ideas is essential to a healthy science and should be facilitated.

Budgets

The US investment in basic nuclear research in FY 1984 will be close to 200 million dollars. This can be compared with the trend in other highly developed coun tries, as shown in figure IV.5-D, which would correspond to a budget of $400-600 million per year. Such comparisons merit serious consideration, not only in nuclear