5: Explore Nuclear Matter — from Quarks to Stars

Understand the evolution and structure of nuclear matter, from the smallest building blocks, quarks and gluons; to the elements in the universe created by stars; to unique isotopes created in the laboratory that exist at the limits of stability, possessing radically different properties from known matter.

Other Information:

Executive Summary: Great strides in our understanding of nuclei and nuclear reactions have led to such profound influences on society as the discovery of fission and fusion and the development of the now vast field of nuclear medicine. With technological advances in accelerators, instrumentation, and computing, we will explore new forms of nuclear structure and matter, and at last unlock the mystery of how protons and neutrons, the basic building blocks of matter, are put together. This knowledge is vital to research in energy and national security, and to understanding the stellar processes that give rise to the known elements in the universe. Detailed Commentary: Nucleons were born in the first minutes after the “Big Bang” and their subsequent synthesis into nuclei goes on in the ever-continuing process of nuclear synthesis in stars and supernovae. Nuclear matter makes up most of the mass of the visible universe. It is the stuff that makes up our planet and its inhabitants. Nuclear matter was once inaccessible for humans to study, but in the first half of the 20th Century, great strides in our understanding of nuclei and nuclear reactions were rapidly made, leading to such profound influences on society as the discovery of fission and fusion and the development of the now vast field of nuclear medicine. Today, understanding nuclear matter and its interactions has become central to research in nuclear physics and important to research in energy, astrophysics, and national security. However, only with the development of the theory of the strong interaction, a strongly coupled quantum field theory called Quantum Chromodynamics (QCD), in just the last few decades, has a quantitative basis emerged to describe nuclear matter in terms of its underlying fundamental quark and gluon constituents. We have only recently acquired more sensitive tools to make the measurements and calculations needed to fully explore this quark structure of the nucleon, of simple nuclei, of nuclear matter, and even of the stars, opening an exciting new era in nuclear physics. The field of nuclear physics can be described in terms of five broad questions: • What is the structure of the nucleon? Relating the observed properties of protons, neutrons, and simple nuclei to the underlying fundamental quarks is a central problem of modern physics. • What is the structure of nucleonic matter? A central goal of nuclear physics is to explain the properties of nuclei and nuclear matter. • What are the properties of hot nuclear matter? When nuclear matter is sufficiently heated, QCD predicts that the individual nucleons will lose their identities and the quarks and gluons will become “deconfined” into quark-gluon plasma; nuclear physicists are searching intensely for this new state of matter at high-energy density. • What is the nuclear microphysics of the universe? How the nuclei of the chemical elements we find on earth were formed in stars and supernovae is a puzzle that relates to our very being. • What is to be the new Standard Model (the current theory of elementary particles and forces)? Precision experiments deep underground and at low energies provide essential complementary information to searches for new physics in high-energy accelerator experiments. Answering these questions will reveal important discoveries about how the visible matter of the physical world around us is put together, how the early universe developed from its initial extremely hot and dense state, the dynamics of stars and other cosmic objects, and how the very elements that we are made of came to be. Vast computing resources will be used to perform the challenging calculations of subatomic structure needed to address these questions, while new accelerators will be needed to study rare nuclei and nuclear reactions at high-energy densities. This research will primarily be performed by international research teams that are a hallmark of Office of Science physics, and will provide world leadership in all the major thrusts of nuclear physics. As an integral part of this Strategic Plan, and in Facilities for the Future of Science: A Twenty-Year Outlook, we have identified the need for five future facilities to realize our Nuclear Physics vision and to meet the science challenges described in the following pages. Two of the facilities are near-term priorities: the Rare Isotope Accelerator (RIA) and the Continuous Electron Beam Accelerator Facility (CEBAF) Upgrade. The RIA will be the world’s most powerful research facility dedicated to producing and exploring rare isotopes that are not found naturally on Earth. The upgrade to the CEBAF at Thomas Jefferson National Accelerator Facility (TJNAF) is a cost-effective way to double the energy of the existing beam, and thus provide the capability to study the structure of protons and neutrons in the atom with much greater precision than is currently possible. All five facilities are included in our Nuclear Physics Strategic Timeline at the end of the chapter and in the facilities chart in Chapter 7 (page 93), and they are discussed in detail in the Twenty-Year Outlook. Our Strategies: In developing strategies to pursue these exciting opportunities, the Office of Science has been guided by the long-range planning report, Opportunities in Nuclear Science (2002), prepared by its advisory panel, the Nuclear Science Advisory Committee (NSAC); and by Connecting Quarks with the Cosmos (2003), a report prepared by the National Research Council Committee on Physics of the Universe. Our Timeline and Indicators of Success: Our commitment to the future, and to the realization of Goal 5: Explore Nuclear Matter—from Quarks to Stars, is not only reflected in our strategies, but also in our Key Indicators of Success, below, and our Strategic Timeline for Nuclear Physics (NP), at the end of this chapter. The NP Strategic Timeline charts a collection of important, illustrative milestones, representing planned progress within each strategy. These milestones, while subject to the rapid pace of change and uncertainties that belie all science programs, reflect our latest perspectives on the future— what we hope to accomplish and when we hope to accomplish it— over the next 20 years and beyond. Following the science milestones, toward the bottom of the timeline, we have identified the required major new facilities. These facilities, described in greater detail in the DOE Office of Science companion report, Facilities for the Future of Science: A Twenty-Year Outlook, reflect time-sequencing that is based on the general priority of the facility, as well as critical-path relationships to research and corresponding science milestones. Additionally, the Office of Science has identified Key Indicators of Success, designed to gauge our overall progress toward achieving Goal 5. These select indicators, identified below, are representative long-term measures against which progress can be evaluated over time. The specific features and parameters of these indicators, as well as definitions of success, can be found on the web at www.science.doe.gov/ measures. Key Indicators of Success: • Progress in realizing a quantitative understanding of the quark substructure of the proton, neutron, and simple nuclei by comparison of precision measurements of their fundamental properties with theoretical calculations. • Progress in searching for, and characterizing the properties of, the quark-gluon plasma by recreating brief, tiny samples of hot, dense nuclear matter. • Progress in investigating new regions of nuclear structure, study interactions in nuclear matter like those occurring in neutron stars, and determining the reactions that created the nuclei of atomic elements inside stars and supernovae. • Progress in determining the fundamental properties of neutrinos and fundamental symmetries by using neutrinos from the sun and nuclear reactors and by using radioactive decay measurements.

Objective(s):

5.1: The Nucleon

5.2: Nucleonic Matter

5.3: Quark-Gluon Plasma

5.4: Nuclear Astrophysics

5.5: Standard Model

Content