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information for an indepth Departmental review of the SSC this Summer. Although a continuing R&D program is required in FY 1987, the direction and emphasis of the program, especially the work on superconducting accelerator magnets and associated systems, will depend on the results of this review.

Nuclear Physics

The Nuclear Physics program supports the basic research necessary to identify and understand the fundamental features of atomic nuclei and their Nuclear processes have guided the evolution of the universe, fueled solar burning, and determined the interplay of the primary forces of

interactions.

nature

force.

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the strong nuclear force, the electromagnetic force, and the weak

The study of nuclear physics consequently lies at the core of fundamental scientific research.

In terms of trained manpower, new knowledge, and advanced instrumentation, the Nuclear Physics program continues to be a vital factor in America's long-term investment in its technological future. Nuclear knowledge, techniques, instruments, and applications are an integral part of American society. These serve as the basis for our national defense strategy, for therapeutic and diagnostic medical applications, for generation of electricity with nuclear reactors (fission now and fusion in the future), and for a large and diverse array of applications in industry.

The role of mesons as nuclear constituents and their utility as nuclear probes continues to be an important component of nuclear physics research, but new theoretical insights have opened the door to a more profound level of understanding. Neutrons and protons are now known to be composed of quarks and gluons, and mesons are now known to be composed of quarkantiquark pairs. Nuclear theorists, along with high energy theorists, are

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investigating the ways in which quarks are confined together in "bags" of three to make up neutrons and protons. A more fundamental theory of the nuclear force is emerging based on the quantum chromodynamics (QCD) model of quarks and gluons. This new theory alters in ever expanding ways the concepts and phenomena of nuclear physics. Exploring these new concepts requires higher energies than have been available to the Nuclear Physics program up to now.

Before turning to the budget request, let me summarize several Nuclear
Physics accomplishments achieved during the last year.

This

The best quantitative measurements for testing the theory that protons and neutrons are made up of quarks come from precision scattering experiments carried out with various high energy beams of electrons and muons. Results of these precision scattering experiments have given detailed information about the quarks and their motion inside the proton and neutron. Recently, the European Muon Collaboration (EMC) at CERN used muon beams to bombard nuclei spanning the periodic table from hydrogen to uranium. Researchers observed that the high energy muons scattered differently from the quarks bound inside nuclei than from the quarks in free protons and neutrons. unexpected observation, called the EMC effect, has been verified and extended by research at the Nuclear Physics facility at the Stanford Linear Accelerator Center. A variety of theoretical models has been proposed to explain the EMC effect. These include (1) an increased size of the threequark bag (nucleon) within the nucleus; (2) the existence of six-quark bags within the nucleus; (3) enhancement of the number of pions within the nucleus; and (4) conventional nuclear structure effects from momentum and binding energy distributions. Since each of these theoretical models can explain the existing electron and muon data, it is important to test with

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further experiments the differences identified in the various models. An experiment using the polarized proton beams at the Los Alamos Meson Physics Facility (LAMPF) now appears to rule out the contributions of increased pion density. A detailed investigation at the Massachusetts Institute of Technology (MIT) Beta Laboratory suggests that interactions between quark motion and bulk nuclear matter correlations may be more important than previously realized leading to enhanced understanding of lower energy phenomena.

In collaboration with experimental groups from the Laboratory for Heavy Ion Research at Darmstadt, West Germany (GSI), and the Universities of Frankfurt and Heidelberg, scientists from Yale have discovered narrow peaks in the spectrum of positron emissions from collisions involving supercritical Coulomb fields. Such fields can occur during the collision of heavy ion projectiles and targets consisting of various combinations of heavy elements. Early experiments indicated that spontaneous ionization of the vacuum was responsible for the production of electron-positron pairs. However, this source of the positrons is being discounted because the position of the peak does not move as predicted with changes of projectile and target species. A second suggestion that the peaks arise from the decay of long-lived super-heavy element formation is also losing favor. Recently, it has been suggested that the peaks could result from the decay of one or more previously unknown light elementary bosons created in the heavy ion collision. Alternative possibilities are that the peaks arise from the decay of a three electron complex consisting of two positrons and one electron or from tidal effects of the atomic electron cloud. Ion source improvements at Argonne National Laboratory (ANL) are being implemented in

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order to investigate this phenomenon with coincidence experiments between the positrons and possible electron partners.

Recent progress at Lawrence Berkeley Laboratory's (LBL) Bevalac includes the first experimental determination of the compressibility of hot nuclear matter by studying the emission of pions from colliding nuclear systems. LBL scientists also made the first measurement of hydrodynamical flow effects in heavy ion collisions. Recent experiments have used the Plastic Ball detector to detect and measure over one hundred particles simultaneously emitted when nuclei accelerated to high energy collide with nuclei stationary in the laboratory. These programs mark the beginning of quantitative studies to determine the equation of state of hot, dense nuclear matter. Knowledge of the nuclear equation of state, in particular the compressibility of nuclear matter, determines our ability to understand collapsing stars as they consume all of their nuclear fuel. Astrophysical calculations require that nuclei have a "soft" equation of state (very easily compressed) in order to bounce back from a gravitationally driven implosion, creating a shock wave that may lead to a supernova explosion. Results from high energy heavy ion collisions, however, indicate that nuclear matter is very "hard." This disparity leads to a distinct, unresolved scientific dilemma.

Recently, the elastic scattering of electron-type neutrinos from electrons was measured for the first time by scientists using the beam stop at LAMPF as an intense source of electron-type neutrinos. In about six months of data taking, over 30 billion neutrinos passed through the detection apparatus in order to produce 51 scattering events. Three distinct possible results were permitted by various theoretical models prior to this result, but only one is consistent with the observation. The experiment is

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continuing, and with the expected level of statistics, further definitive statements about characteristics of the electroweak interaction will be

made.

The FY 1987 Nuclear Physics experimental program will continue its emphasis on the fundamental properties of nuclear matter and on the experimental investigation of the behavior of quarks inside nuclei and of the way in which quarks determine the characteristics of nuclei. In nuclear theory, emphasis in FY 1987 will be on understanding the limitations of the present quantum chromodynamics theories as exact theories of the nuclear force, on improving these theories, and on understanding the ways in which new quark configurations would become evident.

FY 1987 Nuclear Physics Budget Request

The FY 1987 budget request for the Nuclear Physics program is $224.2 million. Of that amount, $174.9 million is for Operating Expenses; $16.0 million is for Capital Equipment; and $33.3 million is for Construction (Table 4). The FY 1987 request includes $25.0 million for initiation of construction plus $6.25 million in operating expense funds for supporting research and development of the Continuous Electron Beam Accelerator Facility (CEBAF). CEBAF has the highest priority for new construction in basic nuclear research in the United States.

CEBAF will be a new, single-purpose facility for basic nuclear research. Its combination of continuous beam, high intensity, and high energy will be unique in the world and will be important to maintain America's position of worldwide leadership in basic nuclear research. It will be operated as a user facility serving a nationwide and international community of nuclear scientists. The central instrument of CEBAF will be a high intensity, high