Download Nuclear Physics Comparative Review and more Exams Nuclear Physics in PDF only on Docsity!
Nuclear Physics Comparative Research Review
for the U. S. Department of Energy
October 31, 2013
1. Introduction
From the middle of May through the end of June of 2013, the Nuclear Physics (NP) Comparative Research Review (CRR) was carried out under the initiative of the U. S. Department of Energy (DOE). The research efforts of 170 university groups and 30 national laboratory groups were assessed on the basis of equally-weighted evaluation criteria. The DOE funding supports approximately 92% of the research in the field of nuclear physics in the U.S., whereas the remainder is mostly supported by the National Science Foundation (NSF). As of today, nuclear physics research, which is our main review topic, receives approximately $162M in support, whereas the total amount of DOE funds, including operation budgets for the facilities for nuclear physics, is approximately $519M.
The DOE is responsible for the strategic planning of the nuclear physics programs in the U.S. which are DOE-supported. It has to identify scientific opportunities for discoveries and advancements, and it also has to build and operate forefront facilities to allow for these opportunities. In addition, it has to develop and support a research community that produces a significant outcome. The results of the NP CRR will help optimize the research portfolio and enable the DOE to work with other agencies to optimize usage of U.S. resources.
The mission of the review panels was to assess the following for each research group:
- Significance and merit of the group’s research, in the context of present and emerging research directions within nuclear physics;
- Future prospects for achieving scientific excellence based on the group’s past achievements and the vigor and focus of the group members;
- Scientific productivity of each group, including any specific strengths and weaknesses;
- Impact of the group’s scientific research effort nationally and internationally;
- Effectiveness of the group in training the next generation of scientists; and
- Particular strengths of each group, such as scientific leadership, technical leadership,
development of innovative concepts or instruments, maintenance of unusual skills, or crucial inputs into collaborative efforts.
During the review the panel identified (i) new insights and/or advancements in the fields of basic science; (ii) new and accumulated knowledge; (iii) well-developed and fore-front technology; and (iv) a very talented and well-trained workforce who would contribute to the DOE’s mission and the U.S. nuclear science-related endeavors.
The review was carried out by five panels, each one consisting of about 10 panel members. The Chair of the review (Shoji Nagamiya of RIKEN/KEK) worked with members throughout all sessions. Names of the panel members are listed in Appendix I. The panel members had access to the submitted written material of the research groups and were present for all oral presentations by the research groups. Each research group gave a presentation of its work followed by a question and answer session. Since the panel members were mostly from outside the U.S., various topics on the U.S. nuclear physics programs were discussed from an international perspective, in addition to general scientific and diversity issues.
2. Premises
The DOE started planning the Comparative Research Review in the fall of 2012. The review took place during five weeks from May 20 through the end of June of 2013 with a week’s break in between.
The exercise was a retrospective review of the quality and scientific impact of NP- supported research efforts for the time period January 1, 2010 – April 30, 2013. The review panels did not consider the relative priorities of the different scientific subfields within the NP portfolio in its assessment, only the relative competitiveness of research groups within a given subfield. While technical contributions were a relevant component of the quality and impact of a group’s supported research, management of major projects and facilities operations were outside the scope of this review. Research efforts that were not included in this review included the Accelerator R&D Program, the Isotope Program, and the Nuclear Data Program. However, laboratory research funded through SciDAC and theoretical topical collaborations were included.
The panel members were carefully selected. First of all, all the panel members were well recognized in that field and represent an appropriate diversity in expertise. Both experimentalists and theorists were mixed in the same panel, with a larger number of theorists present in the nuclear theory panel and a larger number of experimentalists present in the
3. Procedures
The different subfield panels were assigned the following meeting dates:
Nuclear Structure/Nuclear Astrophysics (NSNA): 5/20 – 5/24, 2013 Heavy Ions (HI): 5/28 – 5/31, 2013 Medium Energy (ME): 6/10 – 6/14, 2013 Nuclear Theory (NT): 6/17 – 6/24, 2013 Fundamental Symmetries (FS): 6/25 – 6/28, 2013.
Each panel had about 30-60 groups to evaluate. The evaluation took place in the Washington D.C. area. The programs of all reviews are listed in Appendix II. The allotted times for presentations were: 30 minutes (20 + 10) for groups with 1–2 faculty members, 45 minutes (30 + 15) for groups with 3 faculty members, 60 minutes (40 + 20) for groups with 4 or more faculty members and 75 minutes (50 + 25) for national laboratories.
The Chair’s mission was to ensure that a common standard was used by all panels, and that the assessments of the panels were consistent and fair. Yet, this CRR is based on individual scores provided by each panel member.
Each panel had one Co-Chair, who had the responsibility for the technical conduct of the panel session: for keeping the time and ensuring fairness, for leading the discussion periods and ensuring that the discussion was focused on the criteria of the review. For efficiency, the Chair and Co-Chair also assigned discussion leaders for various packages to ensure that discussions were not missing points. All panel members actively participated in the review and read carefully all the packages that were submitted.
Figure 1: The number of reviewed groups in each subfield panel.
0
10
20
30
40
50
60
70
Nucl Struct / Nucl Astro
Heavy Ions Medium Energy
Nuclear Theory
Fundamental Symmetries
At the end of each day, a summary discussion regarding the reviews of individual presentations was conducted. In order to dynamically assess the progress of the review, daily feedback concerning the scoring was given to the panel members, which helped the discussion and lead to the desired differentiation between groups based on the criteria for the review.
The number of reviewed groups in each subfield panel is shown in Figure 1. The largest subfield was the NT program which contained 62 university and national laboratory groups.
4. Review Criteria
After reviewing the briefing packages, and hearing and discussing presentations, the panel members were asked to score each individual research effort on a scale of 1 (lowest) to 10 (highest) for the following 6 criteria:
- Significance and merit of the group’s research, in the context of present and emerging research directions within nuclear physics.
- Future prospects for achieving scientific excellence based on the group’s past achievements and the vigor and focus of the group members.
- Scientific productivity of each group, including any specific strengths and weaknesses.
- Impact of the group’s scientific research effort nationally and internationally.
- Effectiveness of the group in training the next generation of scientists.
- Particular strengths of each group, such as scientific leadership, technical leadership, development of innovative concepts or instruments, maintenance of unusual skills, or crucial inputs into collaborative efforts.
The panel members were asked to use the full dynamic scoring range available to differentiate between the various groups. In assessing productivity and impact, the panel was also encouraged to roughly normalize according to the resources provided to each group. Thus the “figure of merit” for such metrics should be “d(Physics)/d(dollar)” integrated over the above time period.
In addition, it was highly encouraged by DOE to add written comments, even short ones, to justify or help the NP Office understand why individual panel members scored certain numbers.
produces world-leading results, in particular expanding the knowledge about nuclei and their properties at the limit of existence.
Research with ultra-relativistic heavy-ion collisions is led by the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) in the U.S. Program. The discovery of the strongly interacting Quark Gluon Plasma behaving as an almost perfect liquid is an outstanding achievement, together with the discovery of jet quenching, the unexpected large suppression of heavy quarks, etc. With the Large Hadron Collider (LHC) now in operation, many groups have distributed their interest to both the LHC (ALICE, ATLAS, CMS) and RHIC programs. RHIC produces significant results and plays a leading role in the entire field.
The Medium Energy program focuses on the Continuous Electron Beam Accelerator Facility (CEBAF) at Thomas Jefferson National Accelerator Facility (TJNAF), supplemented by the RHIC Spin program, some smaller FNAL experiments, and some participation in other facilities outside the U.S. As major achievements in this subfield in recent years, U.S. scientists significantly advanced the knowledge on the quark and gluon structure of the nucleon (and the nucleus) and the origin of its spin.
The theoretical activities in the U.S. are remarkably broad, rich and strong. We observed significant progress in the understanding of nuclei and nuclear matter made possible by formal developments and modeling, supported by significant computational advances both in hardware and software and guided by experimental results. This encompasses the entire field of nuclear physics, ranging from fundamental studies of hadron structure and dynamics, to ab- initio and QCD-inspired descriptions of light nuclei, to novel approaches to nuclear structure and reactions globally applicable to the entire nuclear chart and often of important astrophysical relevance.
Finally, an important aim in the field of fundamental symmetries, such as neutrino-less double beta decay, neutron EDM, Project 8, etc., is precision measurements of quantities probing physics beyond the current Standard Model. Some of these topics still require time to obtain results, and all of them attract a large number of students.
International Usage of Facilities
The radioactive-ion beam facilities of the ATLAS at ANL and the NSCL at MSU, together with the RHIC at BNL, and the CEBAF at TJNAF, provide world-class facilities for the U.S. nuclear physics program. Based on these and planned next generation facilities like Facility for Rare Isotope Beams (FRIB), and the complementary university-based cyclotron laboratories, the U.S. nuclear physics community supports a forefront research program.
Several new facilities outside the U.S. have recently become operational or are under
construction. Among these are the RIKEN RI Beam Facility and J-PARC in Asia, FAIR, HIE- ISOLDE, SPIRAL-2, ESS in Europe and the new accelerators at TRIUMF. Furthermore, the relativistic heavy-ion program at the CERN experiments (ALICE, ATLAS, and CMS) will further benefit from the LHC energy increase and the planned upgrade program.
International usages of these facilities will have to be considered to optimize the U.S. nuclear science program.
Strength of National Labs and Synergy Effects
Several panel members were impressed by the strength of research efforts at the national laboratories (ANL, BNL, TJNAF, Los Alamos National Laboratory (LANL), Lawrence Livermore National Laboratory (LLNL), Lawrence Berkeley National Laboratory (LBNL), ORNL). Even those laboratories without a large accelerator play a major role for the nuclear physics community by providing computer resources, major detector laboratories, technical staff or other relevant infrastructures. The strong involvement of university groups, in particular at top institutions, is mandatory to attract bright students into the field and to provide well-trained students. The panel also notes close collaborations of scientists at national laboratories and universities in research, as well as detector design and construction, computer simulations, preparation of materials. This very positive synergy effect between groups at the national laboratories and universities strongly contributes to the success of nuclear science in the U.S.
Joint Positions and Positions at the Top-Level Universities
The panel observed that the research strength in the U.S. is leveraged by the joint appointment system between national labs and universities. A typical example is TJNAF, which provides positions at many surrounding universities to support their faculties and students. In this way, both the neighboring universities and the laboratory benefit from the leveraged research efforts. The RIKEN-BNL Research Center is another strong example, serving as a doorway for junior researchers that obtained later high-level positions at universities all over the world.
While this joint appointment system is a success, the panel also noted that top-level universities are gradually losing nuclear physics faculty positions. Some panel members expressed strong concerns on this point.
6. Statistics
The scoring was performed based on the process described under Section 4 above. Every
discussed any large deviations. This ensured that the entire score distributions was balanced and well justified. The scoring scale ranged from 1 (lowest) to 10 (highest). Below are the score distributions for each panel. The average is 5.6 - 6.0 and the distribution is slightly narrower for “Medium Energy” and “Fundamental Symmetries”. For “Heavy Ions” the distribution has two peak structures. Nevertheless, the average score is very similar for all panels.
7. Individual Panel Summaries
Each panel summary statements resulted from the activities developed in each separate panel.
Nuclear Structure and Nuclear Astrophysics
Overview
In the last two decades, the field of nuclear structure and nuclear astrophysics has undergone a renaissance, thanks to the availability of radioactive ion beams (RIB). Nuclear structure can now be probed at the extremes of the N-Z plane, enabling precision studies of phenomena such as halo nuclei, appearance of new magic numbers, shape-coexistence, isospin dependence of the nuclear force, etc. Nuclear astrophysics has also immensely benefitted from the new era of RI beams. The nuclear reactions that take place in novae as well as in the primordial universe immediately after the Big Bang can now be studied at the relevant energies. As mentioned in Section 5, many U.S. groups have been in the vanguard of this effort, exploiting the complementary facilities NSCL at MSU, ATLAS at ANL, and HRIBF at ORNL, and exploiting major advances in instrumentation such as GRETINA and HELIOS.
The provision of stable beams has also enabled many important discoveries at the ATLAS at ANL and 88" Cyclotron at LBNL and, thanks to the world-leading gamma-ray spectrometer GAMMASPHERE and the recoil separators FMA and BGS. These instruments have proved crucial for studies of high-spin phenomena and exotic and super-heavy nuclear systems. The Centers of Excellence at Texas A&M University (TAMU), Triangle University Nuclear Laboratory (TUNL) and A. W. Wright Nuclear Structure Laboratory (WNSL) at Yale University have provided outstanding opportunities in nuclear structure and nuclear astrophysics research, while training a large number of graduate and undergraduate students.
The panel was impressed by the high quality of many of the groups. This includes the national laboratories as well as university-based groups, where the latter sometimes consists
of only one or two staff persons. Many of the university and laboratory groups have recently hired excellent junior new faculty and staff members, respectively. It was especially encouraging that several of these new faculties gave outstanding presentations to the panel.
Nuclear structure and nuclear astrophysics are experiment-based sciences that have made major advances because of the strong synergy between experiment and theory: the panel observed many cases where experiments were performed in order to test nuclear theory. The panel also noted that the experimental program is providing excellent hands-on experience for the future generation of scientists. In this respect, most groups are able to play this very important role in preparing the next generation of nuclear scientists, although the number of students, relative to staff, was surprisingly variable.
Highlights
- The low-energy community has developed a suite of state-of-the-art instrumentation to best address important questions about nuclear structure and the production of nuclei in stellar environments. The panel noted a number of areas where DOE-supported groups have made outstanding contributions:
- Studies of neutron-rich nuclei in order to probe the nucleon-nucleon interaction, using HELIOS (unique world-wide) and GRETINA;
- Precision measurements of electromagnetic transition rates in light nuclei that provide stringent tests of ab-initio theory, thanks to the strong collaboration with theorists;
- Measurements of single-particle structure near the exotic doubly-magic nuclei 100 Sn and (^132) Sn, using α-decay with stable beams and direct transfer reactions with RIB respectively;
- Discovery of a new region of collectivity around N~40 and Z ≤ 26;
- Measurement of the 2+^ Hoyle state in 12 C that plays a central role in understanding the cluster structure of the 0 +^ Hoyle state;
- Advances in making measurements of the astrophysically important 12 C(α,γ)^16 O reaction, by applying bubble chamber techniques in inverse kinematics;
- Advances in the application of indirect methods to measure key reaction rates in nuclear astrophysics. Most of the nuclear reactions relevant for nova nucleosynthesis are now based on experimental information. We are beginning to achieve a similar result for models of X-ray bursts and core-collapse supernova;
- Precision measurements of nuclear masses for most of the nuclei relevant for the rp- process. Such measurements are starting to approach the r-process nuclei in the region around N ~ 82.
Opportunities
The U.S. program in nuclear structure and nuclear astrophysics is very competitive world-wide, and in some areas world-leading. The new RIB facilities CARIBU and ReA have a window of opportunity before HIE-ISOLDE becomes operational in ~ 2015 and ARIEL and SPIRAL-2 later in this decade. ReA3 and CARIBU will be unrivalled for the provision of refractory element beams of spectroscopic quality. GAMMASPHERE will remain the γ-ray spectrometer of choice for many applications, world-wide. The high- resolution tracking spectrometers GRETINA and the early-implementation of AGATA have similar capabilities to each other. However, the solid-angle coverage of both of these tracking arrays means that they perhaps can only be fully exploited at in-flight facilities. The U.S. groups have made and will make good use of the fast radioactive beams at NSCL, and are preparing to exploit the facility at RIBF (RIKEN); competition from FAIR is planned to come at the end of this decade, at the earliest. In the area of nuclear astrophysics, the LENA and HIγS facilities will remain highly competitive. The U.S. groups also have well-established collaborations with ISAC (TRIUMF).
Relativistic Heavy Ions
Overview
After the discovery phase at RHIC, the field of relativistic heavy-ion (HI) collisions is now focusing on precision measurements to characterize the properties of the strongly interacting Quark Gluon Plasma (sQGP). The field benefits from the unprecedented opportunities offered by five large experiments operating at two outstanding facilities and copiously producing high quality results (the PHENIX and STAR experiments at RHIC and the ALICE, ATLAS and CMS experiments at the LHC). The complementarity of these two facilities, combining the flexibility of RHIC with the energy frontier of the LHC, and the precision measurements foreseen in the near term, ensure productive and exciting research in the next decade with profound insights into the properties of the sQGP.
The U.S. groups involved in HI collisions play a leading role in forging the research program in this area. During the period of this review, the productivity and vitality of the U.S. groups, measured in terms of publications, PhD theses and new faculty positions, are outstanding. Given the short-term perspectives and opportunities there is every reason to believe that these high standards will be maintained in the next few years.
Highlights
- In the decade preceding the period of this review, experiments carried out at RHIC made significant discoveries that brought profound paradigm changes in our concept of the Quark Gluon Plasma (QGP). Instead of the expected gas of free quarks and gluons, the QGP was found to be strongly interacting, behaving as an almost perfect liquid with the lowest shear viscosity to entropy density ratio (η/s) ever measured and approaching the conjectured quantum limit derived in the framework of AdS/CFT. This synergy between experimental HI physics and string theory is one of the totally unexpected and remarkable developments of the RHIC program.
- Among the prominent results obtained at RHIC in that period are the large elliptic flow of particles with values close the ideal hydrodynamic limit, the jet quenching, (first discovered in the suppression of high p (^) T particles, further studied in two-particle correlations and being precisely characterized now using fully reconstructed jets) and the unexpected large suppression of heavy quarks.
- The study of cold nuclear matter effects, using d+Au and p+Pb collisions at RHIC and LHC, respectively, necessary for a quantitative understanding of the nucleus-nucleus collisions, is becoming a topic of great interest in its own right. Surprising results were recently reported raising the question of whether p,d+A are the proper reference to study cold nuclear matter effects.
- The period of the review coincides with the beginning of QGP exploration at the new energy frontier opened with the start of LHC operations in 2010. In two one-month long runs in 2010 and 2011, ALICE, ATLAS and CMS produced an unprecedented wealth of high quality results, confirming the main paradigms established at RHIC and substantially increasing the research scope in terms of p (^) T reach and new observables.
- At the same time, RHIC continued to produce outstanding results: first insights into the plasma temperature derived from the measurements of direct photons, first measurements of low-mass dileptons, first hints of Color Glass Condensate as doorway state toward the formation of the QGP in AA collisions, first results from the BES (Beam Energy Scan) in the quest for a possible critical point in the phase diagram of nuclear matter.
- The current emphasis in heavy ion physics is on precise measurements to characterize the properties of the sQGP. Sometimes, it is necessary to perform the same measurement at the energy regimes of the two facilities to answer specific questions or to scrutinize or constraint theoretical models. For example, is the fluid perfection the same at RHIC and LHC? Or in other words is the η/s ratio (that characterizes the sQGP as a perfect fluid) the same at RHIC and LHC? Initial conditions are presently limiting the accuracy in the determination of this quantity. Combining the elliptic flow results with the higher order flow harmonics is expected to provide tighter constraints in the determination of η/s.
- Another example is the determination of the Debye screening length through the measurement of J/ψ suppression that remains elusive due to competing mechanisms. It is only the systematic study of charmonia and bottomonia states over a large energy range
Concerns
A premature cessation of RHIC operations, that could be imposed, not on scientific grounds, but as a result of the U.S. economic climate, is by far the main concern and will have irreversible devastating consequences for the entire field.
International perspectives
The U.S. university groups and national labs involved in HI physics played and are playing, a leading role in shaping the HI research program worldwide, both at RHIC and the LHC. They have a very strong standing in the HI international community providing scientific and intellectual leadership. They are leading not only the PHENIX and STAR experiments, but also the ATLAS and CMS HI programs. In ALICE, U.S. groups have had a very significant impact on the first data analyses and are among the leading groups in the experiment.
Medium Energy
Overview
Physics has been very successful in identifying the fundamental building blocks of nature. At the first level of complexity, when these building blocks join to form real-world particles, our understanding already falters. After the Higgs confirmation at CERN, the non- perturbative sector of QCD is the last fundamental puzzle of the Standard Model. The study of particles composed of quarks and antiquarks and their governing properties and forces are at the core of the medium energy physics program. Experimental strategies addressing this rely world-wide on six major facilities, CEBAF/TJNAF, BNL/RHIC, BES, J-PARC, KEK and, in the intermediate future, FAIR. To achieve an understanding and a quantitative description here is the big challenge for physics in the years to come.
The basic underlying interaction between quarks can be described successfully in the perturbative regime by the field theory Quantum Chromodynamics (QCD), but this description starts to fail when the distance among quarks becomes comparable to the size of the nucleon, the characteristic dimension of our microscopic world. In the evolution of the universe, some microseconds after the Big Bang, a coalescence of quarks to hadrons occurred which was associated with the generation of mass. The elementary light quarks, the so-called up and down quarks that make up the nucleon, have very small masses that amount to only a few percent of the total mass of the nucleon. Most of the nucleon mass, and therefore of the visible universe, comes from the QCD interaction itself. This generation of mass is associated with the confinement of quarks and the spontaneous breaking of chiral symmetry, one of the
fundamental symmetries of QCD in the limit of massless quarks. The composition of nucleons from quarks and gluons has been a puzzle for the past several decades and tremendous efforts world-wide have been made to try to solve it.
While high-energy physics tries to understand the fundamental aspects of nature by pushing the energy frontier, medium energy nuclear physics concentrates on the precision frontier. The experimental research programs cover a broad field, ranging from the search for exotic forms of matter, such as glueballs or hybrids, to studies of the quark and gluon structure functions obtained in polarized deep inelastic scattering; from meson and baryon spectroscopy to short-range correlations in nuclei to tests of the electro-weak Standard Model. Progress in understanding the strong interaction will have an impact on astrophysical questions, e.g. the physics of neutron stars. The detector technology developed for hadron research paves the way for research beyond the Standard Model, for example the new approaches to the electric dipole moment of the nucleon or dark matter searches.
Highlights
- Important constraints on Δg (the gluon contribution to the nuclear spin) from inclusive polarized pp scattering have been achieved at RHIC.
- The completely unexpected drop of the proton's electric form factor (GEP) with increasing momentum transfer as observed in recoil polarization measurements at TJNAF. This result has started a "cottage industry" of experiments to test the contribution of two- photon exchange radiative corrections to the previous Rosenbluth extractions of GEP which did not show this trend. This discovery contradicts assertions which have been in the textbooks for almost 50 years.
- New data on the anti-quark contribution to the proton spin (Δu-bar, Δd-bar) have arisen from W production in polarized pp scattering at RHIC.
- Precision measurement of the neutral pion decay rate in the PRIMEX experiment at TJNAF, confirming the validity of the chiral anomaly.
- An intriguing similarity has emerged from the comparison of deep inelastic scattering from nuclei (the so-called EMC effect) with ratios of high Bjorken x nuclear structure functions at TJNAF. These data appears to highlight the importance of the local density of nuclei in defining their short-distance structure.
- Important constraints have emerged on the possible contributions from strange quarks to the nucleon's electromagnetic structure through parity violating electron scattering at TJNAF.
- At TRIUMF, achievement of an order of magnitude reduction in the uncertainties for the Michel parameters in muon decay, which play a key role in determining the structure of the Electroweak currents.
developments that play a crucial role in future experiments. The university groups have a major influence in the planning and running of experiments and in providing scientific leadership and spokespersons for the experiments. It is the universities that provide the "new blood" in the form of graduate and undergraduate students. Some institutions only have undergraduate programs, often for minority students. It is important that these groups can participate in fore-front research by being supported by DOE grants.
Concerns
The groups reviewed are highly professional and focused on research at domestic facilities. Given the complexity of the field, the groups should consider increased international collaboration abroad as a means to optimize the U.S. program.
International Perspectives
Medium energy physics has become a center of focus across Asia and Europe, where major investments in facilities have been done recently or are underway. The U.S. medium energy community currently, and in near future, have excellent national labs allowing groups to do world-class forefront research. Also, BNL and TJNAF attract international researchers from other countries to participate in attractive experimental programs.
Nuclear Theory
Overview
During the last two decades there has been impressive progress in nuclear theory due to novel and refined models and to computational advances both in hardware and software, with key guidance from experimental findings. This progress encompasses the entire field of nuclear physics, ranging from fundamental studies of hadron structure and dynamics, to ab-initio and QCD-inspired descriptions of light nuclei, to novel approaches to nuclear structure and reactions globally applicable to the entire nuclear chart, to deep insight into the behavior of dense and hot nuclear matter produced in ultra-relativistic heavy-ion collisions and into the origin of the elements in the Universe in a combined effort of nuclear and astrophysics. With strong support by DOE, the U.S. nuclear theory community has contributed significantly and often decisively to these advances. It impresses by its broad scientific scope as well as by the high quality of most of its individual groups.
Nuclear theory research is intimately related to the experimental efforts and programs at the current and future U.S. flagship facilities TJNAF, RHIC and NSCL/FRIB. The progress achieved in all facets of nuclear physics reflects the close and intertwining relation between
experiment and theory and is made possible by strong theoretical efforts in groups at the ANL, BNL, TJNAF, LANL, LBNL, and ORNL national laboratories and at many universities. The involvement of strong university groups, in particular at top institutions, is mandatory to attract bright students to nuclear topics. The panel emphasizes that a prerequisite for the success in the field is the education of well- trained students at the universities. They are the basis for the next generation of nuclear scientists who can help address important U.S. societal concerns.
Many advances in nuclear theory and its applications require the availability of large-scale computational resources. Here the SciDAC initiative has played a crucial and innovative role by stimulating close collaborations between nuclear researchers, computational scientists and applied mathematicians. This has enabled the optimal use of high-performance computing and has been the basis of much of the achieved progress, not only in nuclear theory, but in related fields such as nuclear astrophysics.
The panel has been broadly impressed not only by the overall strength and quality of DOE-supported nuclear theory, but also by the fact that some of these efforts come from small university groups where the scientific output per dollar invested is often maximized.
Highlights
As noted above, the U.S. nuclear theory community has achieved significant progress in all facets of the field, often leading the world-wide efforts. The panel has noted in particular the following highlights:
- Dramatic advances in lattice QCD (LQCD) physics, including improved actions and algorithms. This has allowed ab-initio investigations of many nucleon properties, such as the origin of the nucleon's spin. More recently, the first calculations are being made of multi-baryon interactions on the lattice. The LQCD efforts have also led to improved understanding of the QCD phase boundary in the search for measures of criticality.
- Descriptions of the structure of hadrons in terms of QCD degrees of freedom as probed in high energy scattering processes. Understandings of geometrical aspects of partonic structure and flavor dependence of electromagnetic form factors, for a large variety of high energy scattering processes have developed considerably. This has been driven by developments in LQCD, continuum QCD models, and their interaction.
- Derivation of nucleon-nucleon (2N) and three-nucleon (3N) interactions respecting QCD symmetries, together with the development and application of microscopic many-body models to nuclear structure and reactions. Green's Function Monte Carlo studies have demonstrated the importance of 3N interactions for the accurate description of structure and transition strengths in light nuclei up to mass 12. Exploiting 2N and 3N interactions, consistently and systematically derived within Effective Field Theory, ab-
