APS Division of Nuclear Physics - Current research topics

Research Highlights

This feature of the DNP Home Page hightlights research topics. The topics rotate on a regular basis and past articles are archived here. If you would like to recommend a research topic for display in this spot, send a draft following our guidelines (PDF) to dnpweb@nscl.msu.edu or contact a member of the DNP Home Page Committee.

Vector Meson Production from Nuclei

Quantum chromodynamics (QCD), the theory of the strong interaction, has been very successful in describing high-energy and short-distance-scale experiments, and less successful in explaining low-energy and large-distance scales. However, the symmetries of QCD (such as chiral symmetry) provide guiding principles in treating the non-perturbative regime.

First MiniBooNE Neutrino Oscillation Results

The MiniBooNE Collaboration reports first results of a search for ? e appearance in a ? µ beam. Using a 40-foot spherical tank filled with 800 tons of mineral oil in the Booster neutrino beam at Fermilab, no signicant excess of events above background is observed for reconstructed neutrino energies above 475 MeV. The data are consistent with no oscillations within a two-neutrino appearance-only oscillation model. However, an unexplained excess of events is observed for reconstructed neutrino energies below 475 MeV.

KamLAND: Studying Neutrino Oscillation with Reactors

The Kamioka Liquid-scintillator Anti-Neutrino Detector (KamLAND) experiment is a reactor anti-neutrino experiment that searches for neutrino oscillation using a baseline that is two orders of magnitude larger than that in any previous reactor measurement. Results to date have shown that some electron anti-neutrinos disappear on their journey from their originating reactor to the detector. KamLAND's latest results also show a distortion in the neutrino energy spectrum that is consistent with neutrino oscillation and strongly disfavors other neutrino disappearance mechanisms. While the Standard Model assumes neutrinos to be without mass, neutrino disappearance through oscillation is evidence that neutrinos do have mass. The KamLAND experiment continues to take data and will provide the most precise determination of Δm₁₂², a key oscillation parameter, in the foreseeable future.

Strange Quarks in the Proton

The most precise measurement yet of strange quarks in the proton, performed at the Department of Energy's Thomas Jefferson National Accelerator Facility (Jefferson Lab) by the second phase of the Hall A Proton Parity Experiment (HAPPEx II), shows that the strange quark contribution to the proton's overall charge distribution and magnetic moment is small. Indeed, it yields no more than 2% of the proton charge radius and less than 4% of its magnetic moment. This result firmly pins down strange quark contributions (at one specific length scale, Q²=0.1 GeV²) to the proton's charge distribution and magnetic form factor, constraining the world experimental data to less than half of its previous range. The HAPPEx II result was a highlight of the Dallas APS Meeting in April 2006.

2005 Nobel Prize in Physics

The 2005 Nobel Prize in Physics was awarded in part to Roy J. Glauber of Harvard University "for his contribution to the quantum theory of optical coherence." Glauber provides an excellent example of the interrelationships between physics subfields. His work on quantum optics is recognized as a major contribution to Atomic, Molecular and Optical Physics (AMO).

A few years before his seminal work on the coherent quantum states of photons, he used the eikonal approximation in his development of a high-energy multiple scattering theory, known as "Glauber theory". This remains a major contribution to High Energy and Nuclear Physics. Glauber's famous 1959 lectures at Boulder, Colorado, developed his widely used theory for evaluating the scattering of protons, or other hadrons, as a sequence of collisions with different nucleons in a nucleus. At high energies, such processes involve multiple diffraction of the incident waves from the individual nucleons, showing a close and beautiful connection with optical diffraction. In addition to his work in quantum optics, Glauber remains interested in high-energy scattering theory.

The 2005 Nobel Prize announcement can be found here.

Laser Spectroscopic Determination of the Nuclear Charge Radius of ⁶He

For physicists the nucleus ⁶He, with 2 protons and 4 neutrons, has been intriguing for quite some time. Measurements in the eighties and nineties have indicated that, when used as a beam, the probability for it to induce a nuclear reaction on any target is much larger than that for ⁴He. This observation was interpreted as a strong indication that ⁶He is a three-body "halo" nucleus, i.e., it can be best viewed as a well bound ⁴He core and 2 neutrons orbiting this core at large distances. Moreover, while these three constituents of ⁶He form a bound system, the nuclear potential is not strong enough to bind any two of them separately. For this reason, ⁶He is often referred to as "Borromean" (The name derives from the heraldic emblem of the medieval princes of Borromeo, three rings interlocked in such a way that the removal of any of the rings will cause the remaining two to fall apart).

The charge radius of ⁶He has been determined for the first time by measuring the atomic isotope shift between ⁶He and ⁴He using laser spectroscopy.

2004 Nobel Prize in Physics

The 2004 Nobel Prize in Physics was awarded to David Gross, David Politzer, and Frank Wilczek for their work on asymptotic freedom, which helped establish quantum chromodynamics (QCD) as the theory of the strong interactions that bind the atomic nucleus. Asymptotic freedom is a property of the interaction between the quarks that make up protons, neutrons, and other subatomic particles. The proton and neutron are strongly bound systems of three quarks, but the interaction between the quarks becomes very weak at short distances, or at high energies.

QCD is a central part of modern nuclear physics research. A detailed understanding of the confinement of quarks, and the role of the gluons that bind the quarks together into observable mesons and baryons is central to the research of intermediate energy physicists. How the nuclear force among protons and neutrons arises from QCD remains one of the most important problems in nuclear physics. Relativistic heavy ion physicists focus on the deconfinement of quarks into a quark-gluon plasma at high temperatures. Nuclear theorists and astrophysicists recent studies include interesting ideas on the properties of QCD matter at high densities and low temperatures, such as is found in neutron stars.

The 2004 Nobel Prize announcement can be found here.

The Spin Structure of the Nucleon in the Valence Quark Region

During a recent experiment at Thomas Jefferson National Accelerator Facility (Jefferson Lab, or JLab), precision data have been obtained, for the first time, on the spin structure of the neutron in the valence quark region. Such data provide an important test of our fundamental understanding of the nucleon structure and the spin/flavor features of the strong interaction. In particular, they suggest the importance of the quark orbital angular momentum in the nucleon spin.

The spin structure of the nucleon has been studied for over thirty years (for a review, see e.g. Adv. Nucl. Phys. 26, 1 (2001)). The first set of data on the proton polarized structure functions from CERN in the late 1980's, combined with earlier data from SLAC, showed that only (12±17)% of the nucleon spin could be attributed to the quark spin. This result contradicted the valence quark model expectation, in which about 75% of the nucleon spin arises from the spin of the three valence quarks. Since the quark model is so successful as a qualitative guide to hadronic study, this observation was so surprising that it was named "the proton spin crisis" -- Where does the rest of the proton spin come from?

From decuplets to anti-decuplets and quarks to pentaquarks

Dozens or even hundreds of protons and neutrons can combine to form the known nuclei of atoms. But when it comes to putting quarks together to form protons, neutrons or other particles, they only come in packages of twos or threes. Or at least so it was thought until recently. For over 30 years, physicists have searched for exotic particles known as pentaquarks, that have a valence structure of four quarks and one antiquark. In the fall of 2002, evidence for a narrow baryon state having an exotic strangeness quantum number, consistent with a pentaquark structure, was presented at the PANIC conference. Since then, many independent experiments have confirmed the existence of this state.

The Charge and Magnetization Distributions of the Proton: G^E_p and G^M_p

Although the protons and neutrons in atomic nuclei account for nearly all of the observed mass in the universe, these particles have a complicated structure that is poorly understood. This situation arises from the fundamental theory of strong interactions, quantum chromodynamics (QCD), which gives the nucleons their very rich structure, but which is also nonperturbative and extremely difficult to solve.

The Sudbury Neutrino Observatory (SNO) and the Solution of the Solar Neutrino Problem

The Sudbury Neutrino Observatory (SNO) is a heavy water Cherenkov neutrino detector located 6800 feet underground at the active INCO, Ltd. Creighton nickel mine near Sudbury, Canada. On April 20, 2002, SNO published results which are thought to have solved the Solar Neutrino Problem.

SNO's photomultiplier array

A view of the exterior of SNO's photomultiplier array during detector construction. Photo courtesy of LBNL.

2002 Nobel Prize in Physics

Raymond Davis Jr. (University of Pennsylvania) and Masatoshi Koshiba (Univ. of Tokyo) shared half of this years Nobel prize in physics. Their citation reads "for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos".

Until we started to understand the nature of the nuclear forces, the origin of solar energy was a mystery. Because of the fundamental work in Nuclear Physics done by Hans Bethe, George Gamow, Willy Fowler, Ray Davis, M. Koshiba their many collaborators, we now know that Sun's energy originates from a series of nuclear reactions going on in its core. These nuclear reactions emit neutrinos which travel through the material in the Sun very easily. Solar models, developed by John Bahcall and others, predict the solar neutrino flux which reaches the Earth.

The other half of the prize was won by Riccardo Giacconi (Associated Universities Inc.) "for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources"

Artist's conception of a binary sytem. Photo courtesy of NASA/HEASARC.

The Nobel Prize for Prof. Giacconi recognizes his enablement of the birth of X-ray astronnomy. This led to the discovery of neutron stars that accerete matter from a binary companion, releasing large amounts of gravitational energy. These objects periodically emit large flashes of X-rays as a result of nuclear reactions taking place in the built-up material. The exact details of what takes place awaits further illucidation of the nature of neutrons stars and the underlying nuclear physics. New nuclear physics facilities such as RIA will make a major contribution to this understanding.

ATTA—A New Method of Trace-Isotope Analysis

Dr. Chun-Yen Chen aligning the optics of the atom trap used to count ⁸¹Kr atoms and demonstrate the new Atom Trap Trace Analysis (ATTA) method. (Photo by George Joch)

Magnetic Trapping of Ultracold Neutrons

Neutron guide hall at the NIST Center for Neutron Research. Here, experimentors from Harvard, NIST, LANL, and HMI have shown they can load ultracold neutrons into a magnetic trap through inelastic scattering of neutrons with phonons in superfluid ⁴He.