Physics Colloquium Schedule

Fall 2003

Abstracts

The Remarkable New BABAR Resonances

Ted Barnes (UT Physics/ORNL)
Stefan Spanier (UT Physics/BABAR Collaboration)

In April of this year the BABAR collaboration announced the discovery of a new strongly interacting particle, the D_sJ(2317)⁺. This was followed by the discovery of a second state, the D_sJ^*(2463)⁺. Both have now been confirmed by other experimental collaborations. The new state contains both charmed and strange quarks, and is much lighter and more long-lived than had been expected for a meson at this mass. In this talk we will review the experimental status of the exciting new discoveries and discuss what explanations theorists have proposed for the discrepancies between their expectations and the measured characteristics.

Computational Physics at the Nanoscale

Jerzy Bernholc (Department of Physics, North Carolina State University)

Nanoscale science has emerged as a major new interdisciplinary frontier, with the potential for ground-breaking advances in many areas of science and technology. Richard Feynman was the first to recognize its promise in a visionary 1959 lecture, but true progress had to await innovations in experimental techniques and instrumentation. With the development of new atomic and nearly-atomic-resolution growth and measurement techniques, nanoscience has become a high-priority research thrust worldwide, with physics playing one of the central roles. New nanoscale phenomena, materials and devices are being investigated, with the hope for revolutionary breakthroughs. However, experimentation at this scale is still very difficult, highlighting the need for reliable and predictive theory to guide and interpret the experimental advances.

At present, it is already possible to predict the properties of "simple" new and artificially structured materials entirely by computations, using atomic numbers as the only input. Although nanoscale presents special theoretical challenges, it should eventually be possible to “design” nanoscale structures with tailor-made properties largely on a computer, with only relatively few final candidates being evaluated experimentally. This goal is still some time in the future, but current calculations can already supply critical information, including that which is difficult or impossible to measure. They can also predict and unravel many nanoscale phenomena. This talk will review the status and prospects of such calculations, using as examples simulations of the structure and dynamics of solid C60, calculations of surface structures and their optical signatures, and predictions of the properties of nanotubes – the strongest material known and a candidate for nanoscale strain and molecular sensors, novel field emitters, and electronic devices.

Why Talk about Accelerators? An Overview of the Field and the Science

Norbert Holtkamp (Director, Accelerator Systems Division, Spallation Neutron Source)

Accelerators have been and continue to be research tools for all flavors of science; high energy physics, nuclear physics and basic energy science. As such the Department of Energy and the National Science Foundation have large and small scale operating facilities and continue to develop ideas and proposals in which accelerators play a key role. At the same time the sophistication in accelerator physics that we have achieved today has led to new accelerator technology and development and higher performance facilities. Because of the size of some of the accelerator projects, national and international collaboration plays a more dominant role in influencing the way accelerators are built. The Spallation Neutron Source (SNS) is a prime example and will be presented during the talk.

Precision Measurements with a Single Trapped Electron

Brian D'Urso (ORNL Engineering Science and Technology Division)

A single electron cooled below 350 mK in a Penning trap can be confined almost indefinitely and is weakly coupled to the external environment. This weak coupling is advantageous for certain precision measurements, such as the electron g factor, even as it makes detection of the motion of the electron challenging. A dilution refrigerator cools the cyclotron motion of the electron into the ground state, and a quantum non-demolition measurement reveals quantum jumps between energy levels of the driven cyclotron motion. Experimental improvements may reduce the uncertainty in the measured electron g factor below one part per trillion.

Filling the THz Gap

Gwyn P. Williams (Jefferson Lab)

Light is one of our prime tools for understanding both form and function of materials, but there is a gap in the electromagnetic spectrum between electronics and photonics. There are compelling reasons to utilize this region for fundamental studies ranging from materials to proteins, studying phenomena as diverse as superconducting band-gaps and protein conformations. The gap is called the THz gap after the light frequency that characterizes it. We will show how particle accelerators can be used to tailor the brightness and time-structure of light in novel ways for unique applications to dynamical and kinetic studies that lead to new fundamental understandings of materials properties in this Thz region.

Making Sense of the New Cosmology

Micheal Turner (University of Chicago/National Science Foundation)

Cosmology is in its most exciting period of discovery yet. Over the past five years we have determined the basic features of the Universe -- spatially flat; accelerating; composed of 1/3rd a new form of matter, 2/3rds a new form of energy, with some ordinary matter and neutrinos; and apparently born from a burst of rapid expansion during which quantum noise was stretched to astrophysical size seeding cosmic structure. Now we have to make sense of all this: What is the dark matter particle? What is the nature of the dark energy? Why this mixture? How did the matter -- antimatter asymmetry arise? What is the underlying cause of inflation (if it occurred)? If we succeed in making sense of our Universe, this will truly be remembered as a Golden Age.

An Overview of High Performance and the Computational Grid

Jack Dongarra (UT/ORNL)

In this talk we will look at how High Performance computing has changed over the last 10-year and look toward the future in terms of trends. In addition, we advocate the `Computational Grids' to support `large-scale' applications. These must provide transparent access to the complex mix of resources - computational, networking, and storage - that can be provided through aggregation of resources. The vision is of uniform, location independent, and transient access to the

Computational
Catalogued data
Instrument system
Human collaborator

resources of contemporary research activity in order to facilitate the< solution of large-scale, complex, multi-institutional/multidisciplinary data and computational based problems. It envisages these resources being accessible through a Problem Solving Environment appropriate to the target community.

Sub-Z Supersymmetry: Precision Electroweak Physics at Low Energies

Michael Ramsey-Musolf (University of Connecticut and Caltech)

The search for physics beyond the Standard Model lies at the forefront of
particle and nuclear physics. This search is being carried out through new
experiments at high energy colliders as well as through increasingly precise
measurements at energies below the mass of the Z-boson. In this talk, I
discuss the role played by these precision measurements and how they may
help us address important questions left unanswered by the Standard Model.
To make the discussion concrete, I focus on candidate for "new physics" --
Supersymmetry -- and show results of several new calculations of
supersymmetric effects below the Z-pole.

Frustration and How to Fight it in Spin Systems

S.-H. Lee (National Institute of Standards and Technology)

Competing interactions are a common feature in physical and biological systems.
Novel and complex phenomena emerge as systems attempt to resolve the
frustration by reorganizing the underlying degrees of freedom. For example, in
high temperature superconductors charge carriers organize into stripes in a
balancing act between antiferromagnetic and Coulomb interactions. An analogous
situation can be found in systems with triangular spin arrangements where all
magnetic interactions cannot be satisfied due to the topology of the lattice
possibly leading to an infinite zero-point entropy. The important issues in
this field are (1) what the nature of the spin liquid phase is and (2) how the
system responds to the ground state degeneracy.

I will address these issues in geometrically frustrated magnets by discussing
the spinel antiferromagnets ZnM2O4 (M=Cr and V). Recently we found by inelastic
neutron scattering that a composite spin degree of freedom emerges in the cubic
spinels. In the gapless spin liquid phase, spins self-organize into weakly
interacting antiferromagnetic hexagonal loops rather than fluctuate
individually. In addition, upon cooling, instead of remaining in the spin
liquid phase, these systems undergo novel phase transitions to relieve magnetic
frustration when the spin degree of freedom is coupled with orbital and/or
lattice degrees of freedom.

Imaging Cancer with Positron Emission Tomography

David W. Townsend (UT Department of Medicine/Director of the Cancer Imaging and Tracer Development Program)

The past few years have seen the transition of Positron Emission Tomography (PET) from the research domain into mainstream clinical applications for oncology. The emergence of PET as the functional imaging modality of choice for diagnosis, staging, therapy monitoring and assessment of recurrence in cancer has led to an increasing demand for this advanced imaging technology. The recognition that functional imaging modalities such as PET may provide an earlier diagnosis and more accurate staging than conventional anatomical imaging has accelerated the acceptance of the technology, particularly as PET imaging is now a reimbursed procedure for many types of cancer. While PET offers an extensive array of different radiopharmaceuticals, or molecular probes, to image different aspects of physiology and tumor biology, currently the most widely-used PET tracer is the fluorinated analogue of glucose, 18F-deoxyglucose (FDG). FDG is taken up in all cells using glucose, including cancer cells. This presentation will briefly describe the physical principles of positron tomography and their impact on the design and performance of PET scanners. Detector technology will be discussed, including the transition to a new scintillator material (LSO) that significantly improves scanner performance. The rationale for the transition from PET scanners to combined PET/CT scanners will be presented and combined PET/CT scanner designs will be reviewed together with a description of the appropriate protocols currently implemented for combined PET/CT studies. All applications will be illustrated with clinical studies.

Order and Quantum Phase Transitions in the Cuprate Superconductors

Subir Sachdev (Professor of Physics, Yale University)

I will begin with a general introduction to the theory of quantum phase transitions. I will discuss applications of this theory to Mott insulators with a spin gap, where quantitative tests of theory are now possible. Then I will apply ideas from the theory to the cuprate superconductors, and show how such an approach has led to systematic predictions for the interplay of various spin and charge orders with the pairing order of the Bardeen-Cooper-Schrieffer theory of superconductivity. I will use this context to review the results of innovative recent neutron scattering and scanning tunnelling microscopy experiments.

Football Physics

Tim Gay (Professor of Physics, University of Nebraska)

This talk is based on a series of one-minute physics lectures given to the 8 x 10⁴ fans that attend the University of Nebraska home football games. The lecture topics range from rigid body rotation to ionizing collisions between linebackers and I-backs. The problem of simultaneous edification and amusement of the fan in the stands is considered. Several useful physics tips for the Vols will be provided. (See the Football Physics Web Site at Nebraska.)

Can Carbon Nanotubes Smell Inert Gas Atoms?

Peter C. Eklund (Professor of Physics/Materials Science and Engineering, Penn State)

The thermoelectric power and resistivity of a rope of Carbon Nanotubes is
dominated by the metallic tubes in the bundle. These metallic tubes are
also a conducting monolayer of carbon atoms, albeit a monolayer that is
wrapped into a long seamless cylinder. Because the conduction electrons
must travel along this surface, adsorbed molecules on the surface might be
expected to have an effect on the electrical properties. In fact, we can
(and have) observed this phenomena, and perhaps this effect is not so
surprising. What is more interesting may be that electrical properties of
bundles of nanotubes are found sensitive to collisions of gas atoms with the
tube walls, i.e., the nanotubes can "smell" their presence. In this
presentation, I will attempt to provide the necessary background to
understand why this result might also be expected, and show the systematics
of the nanotube electrical response to a series of inert gases, N2 and CH4.
We find an M^^1/3 dependence of the thermopower and resistivity on the
colliding atom/molecule mass M for fixed temperature and pressure. Results
of computer simulations of atom-nanotube collisions that suggest an
underlying mechanism for our observations will also be presented.

Attosecond Science

Paul Corkum (Program Leader, Femtosecond Science, Steacie Institute for Molecular Sciences, National Research Council of Canada)

Sub-femtosecond photon or electron pulses were both achieved within the past few years. Experience teaches that the ability to make measurements in any new time regime opens new areas of science. In the case of attosecond pulses, the importance is not only "attoseconds", but the promise of combining sub-Angstrom spatial resolution with sub-femtosecond temporal precision (Attoseconds&Angstroms).

I will describe how attosecond photon and electron pulses are produced and measured, emphasizing the common issues linking them. I will also show how correlation is used to measure the motion of a D2+ vibrational wave packet with combined ~ 200 attosecond, ~0.03 Å precision. Correlation may offer a route to real-time measurement of dynamics of the nucleus.