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Fall 2004

Schedule Fall 2004

September 7, 2004
3:00 pm (Tuesday)

Dr. David Wilkowski
Laboratoire Ondes et Desordre, Nice, France

Cooling of Sr atoms in a magneto-optical trap and experiments on coherent backscattering of light

During the seminar I will present the work done on the experiment of laser cooling of strontium atoms in Nice, France. In the first part, I will present our results on temperature measurements of atoms in a 1D molassas. Because the transition used for cooling is a J=0 to J=1 transition, one expects that only a Doppler cooling mechanism may occur. Hence, those experiments should be a good quantitative test of the Doppler Theory. In fact the measured temperatures are much higher than the theoretical predictions. We find that Doppler cooling is very sensitive to intensity imbalance that leads to extra heating terms, which explains the observed temperature. In the second part, I will discuss the effect of localization of light in a random scattering medium: The cold cloud itself. I will explain why Sr is a good choice for those kinds of experiments. I will also present our results of coherent backscattering of light in the cold cloud and discuss the effects of saturation of the transition.


September 14, 2004
3:00 pm (Tuesday)

Dr. Robert B Wiringa
Argonne National Laboratory

Quantum Monte Carlo Calculations of Light Nuclei

A major goal in nuclear physics is to understand the stability, structure, and reactions of nuclei as a consequence of the interactions between individual nucleons. Realistic NN interactions, which accurately reproduce elastic scattering data, have a complicated dependence on the relative positions, spins, isospins, and momenta of the nucleons.

In addition, there is strong empirical evidence for, and theoretical expectations of, significant many-nucleon forces. These factors make the ab initio calculation of nuclear properties an extremely challenging many-body problem.

Tremendous progress in the solution of light nuclei has been made in the past decade using a variety of many-body methods, aided by rapid advances in computer power. This talk will focus on quantum Monte Carlo methods, including both variational Monte Carlo (VMC) and Green's function Monte Carlo (GFMC). We have calculated more than 80 nuclear ground and excited states (not counting isobaric analogs) for A <= 10 nuclei, and recently the ground state of 12C, using realistic NN and 3N potentials, with an excellent reproduction of the experimental spectrum. Calculations of energy spectra also have been made for a series of progressively simpler interactions, to investigate how certain features, like the lack of stable A=5,8 nuclei, are dependent on different components of the nuclear force.

Additional energy calculations include studies of pure neutron systems, investigating the possibility of a stable tetraneutron, and simulating very neutron-rich nuclei. Many other nuclear properties, such as densities, electromagnetic moments, electroweak transitions, spectroscopic factors, and reactions of interest to both astrophysics and rare-isotope accelerator facilities, are being studied with these methods.


September 15, 2004
4:30 pm (Wednesday)

Note unusual date and time

Dr. Robert B Wiringa
Argonne National Laboratory

A Universe of Nuclei

Dean's Lecture Series - PUBLIC LECTURE

A major goal in nuclear physics is to understand the stability, structure, and reactions of nuclei as a consequence of the interactions between individual nucleons. One of the most basic properties that can be studied, both experimentally and theoretically, is the binding energy of a nucleus, which is the amount of energy required to break up a nucleus into its constituent nucleons. The binding energies of adjacent nuclei determine their relative stability and what radioactive decay modes may be possible. In ab initio calculations of nuclei, one attempts to use realistic nuclear interactions and many-body computational techniques to predict the binding energies. However, an accurate description of two-nucleon interactions requires a very complicated potential function that depends on the relative positions, spins, isospins, and momenta of the particles. In addition there is strong evidence for significant multi nucleon forces. This makes the calculation of nuclear properties an extremely challenging many-body problem.

Tremendous progress in the solution of light nuclei has been made in the past decade using a variety of many-body methods, such as quantum Monte Carlo, aided by rapid advances in computer power. Calculating the properties of the six-body nucleus, 6Li, with realistic forces was a frontline problem in 1995, requiring 2,000 processor hours on one of the most powerful available parallel computers. Since then we have studied all the nuclei up to ten nucleons, and recently we obtained a first solution for the ground state of a twelve-body nucleus, 12C. The latter problem is equivalent to solving 270,000 coupled complex second-order differential equations in 36 dimensions, which is about 5,000 times more difficult than 6Li. However, it required only 70,000 processor hours on a modern machine, reflecting improvements in both algorithms and raw computer power.

Although only the lightest nuclei can be studied at this level of precision, they are of crucial importance to our understanding of the universe. For example, the fact that there are no stable five-body or eight-body nuclei is crucial to both primordial and stellar nucleosynthesis. It leads to a universe whose visible matter is dominated by hydrogen and 4He, with trace amounts of deuterium, 3He, and 7Li. It also enables stars like our sun to burn steadily for billions of years, allowing time for the evolution of life intelligent enough to wonder about such issues.


September 21, 2004
3:00 pm (Tuesday)

Dr. Cynthia Keppel
Hampton University

Biomolecular Imaging in Nuclear Medicine: Improved Cancer Localization, Diagnosis, and Treatment

Some recent biomedical technology development activities will be presented. Specifically, a functional imaging camera for X ray / scintimammography image fusion in stereotactic breast cancer biopsy will be discussed, along with first results from this device in clinical trials. Additionally, a novel approach to real-time brachytherapy radiation dose distribution measurement will be introduced, along with other technologies if time permits. In all cases, the devices represent applications of nuclear and particle physics detection techniques to radiological medicine.


September 28, 2004
3:00 pm (Tuesday)

Dr. Sebastian Kuhn
Old Dominion University

The Structure of the Neutron - what do we know already, and how can we learn more?

Inaugural Lecture

Neutrons are one of the two basic building blocks of all atomic nuclei making up our world. While we know a great deal about the interior structure of their brethren, the protons, data on the neutron are much more sparse and less precise. This is mostly due to the fact that neutrons cannot be accumulated in large numbers into suitable "targets" which would allow us to study them with accelerator beams (as we do routinely with protons in the form of ordinary hydrogen). Instead, we have to use nuclear targets - typically heavy hydrogen (deuterium) or Helium-3, which results in complications and uncertainties from nuclear physics effects.

In my talk, I will discuss some of the methods used to circumvent or at least mitigate some of these complications, and some of the information we already have on the neutron. I will then present a new experimental program to study the neutron structure with minimal nuclear physics uncertainties, which will take place at Jefferson Lab's CLAS detector within the next couple of years. I will conclude with an outlook for the more distant future.


October 5, 2004
3:00 pm (Tuesday)

Dr. Alexander Fridman
Drexel University

Non-Thermal Atmospheric Pressure Plasma: Physics and Applications

Experimental and theoretical investigations of the major non-equilibrium atmospheric pressure discharges: pulsed corona, dielectric-barrier discharge (DBD), gliding arc and atmospheric pressure glow (APG) are to be discussed. Special attention will be paid to problems of transitions between homogeneous and filamentary modes of DBD/APG, and between thermal and non-thermal regimes of gliding arcs. Applications to be discussed include air and exhaust gas cleaning from volatile organic compounds (VOC) and other pollutants, fuel conversion and hydrogen production, ignition and stabilization of flames, and sterilization.


October 19, 2004
3:00 pm (Tuesday)

Dr. John Huth
Harvard University

Scientific Computing and the Grid

The need for large experimental facilities and shared data has driven the size of scientific collaborations to unprecedented sizes. In some cases, collaborations number thousands of physicists. These groups must manage their distributed computing and data handling needs across wide area networks in a coherent and manageable way. An emerging technology, grid computing, is being employed by a number of scientific communities in response to these trends. Grid computing is still in its infancy, yet provides substantial promise for the next world-wide-web. This talk explores the concepts and realities of grid computing, with particular emphasis on the use of the grid by high energy physicists.


October 20, 2004
3:00 pm (Wednesday)

Note unusual date

Dr. John Huth
Harvard University

The Wisdom of the Inward Parts: Science at the Frontiers of Scale

Dean's Lecture Series

Physics and astronomy have progressively expanded the scales of discovery into the large and the small. Particle accelerators have probed smaller and smaller distance scales until we are on the verge of understanding the unification of the fundamental forces of nature. Telescopes, measuring electromagnetic waves over a large range of frequencies, are able to see the largest structures of the universe, providing a glimpse of the conditions almost immediately after the big-bang. Our understanding of the largest and smallest structures have come together to provide a compelling picture of the universe. Yet, many fundamental puzzles remain unsolved, suggesting factors at play that leave us searching for explanations.


October 26, 2004
3:00 pm (Tuesday)

Dr. Reiner Dreizler
Institut für theoretische Physik, Frankfurt

Density Functional Theory: An Approach to the Quantum Many Body Problem that Works

Density functional theory has become a mainstay for the investigation of quantum many body systems such as solids, molecules, atoms and nuclei. The talk will provide an overview of this active field of research covering the foundation and basic statements of the theory, the quest for appropriate functionals and a sample of results obtained for the systems indicated.


October 27, 2004
3:00 pm (Wednesday)

Note unusual date

Dr. Reiner Dreizler
Institut für theoretische Physik, Frankfurt

Numerical Simulations: From Tailor-made Materials to Protein Folding

Dean's Lecture Series

Computer simulations can be considered as a link between analytical theory and experiment. After a brief outline of the history of computing facilities within the academic lifetime of the speaker, a selection of computer simulations of physical and chemical systems such as materials research, the structure of amino acids and the problem of protein folding will be discussed. This is to be followed by a very brief outline of some standard methods used in computational physics.


November 2, 2004
3:00 pm (Tuesday)

Dr. H.R.J. Walters
Queens University Belfast

Pseudostate Methods in Electron -, Positron -, and Positronium - Atom Scattering

I shall begin with a historical perspective on pseudostate methods. The pseudostate idea will then be explained in greater detail and techniques used to construct pseudostates will be discussed. Applications to differential ionization, in particular to (e,2e) and (e,3e), and to positron - atom and positronium - atom scattering will be shown.


November 3, 2004
3:00 pm (Wednesday)

Note unusual date

Dr. H.R.J. Walters
Queens University Belfast

Atomic Collisions Involving Positrons

Dean's Lecture Series

In this talk my aim will be to give a flavour of areas of interest and to convey the spirit of the subject. I shall briefly cover the following areas : bound states; positron - and positronium - atom scattering; positronium - positronium scattering; cold antihydrogen; annihilation.


November 9, 2004
3:00 pm (Tuesday)

Dr. Lee Collins
Los Alamos National Laboratory

Ultracold Phenomena from Plasmas to Atomic Optics

POSTPONED

The advent in the last few years of sophisticated techniques for trapping and imaging gases at ultracold temperatures (< 1 mu-K) has opened a vast field of research in such phenomena as Bose-Einstein condensates (BEC), superfluidity, solitons, and Rydberg gases. Two particularly fruitful areas have centered on atom optics and ultracold plasmas (UCPs). The coherent nature of BECs invites analogies with standard optics; an interesting example is the BEC interferometer[1], in which quantum mechanical effects permit enhanced sensitivity.

A very cold gas, ionized by a laser, can display many features of a strongly-coupled plasma, in which the interparticle interactions dominate the thermal component, even though the densities remain extremely low. These ultracold plasmas[2], produced in table top experiments, can serve as laboratories to probe quantitatively many basic plasma effects such a recombination mechanisms and coherent structure (waves). For example, understanding the evolution of these UCPs is essential for devising mechanisms to produce antihydrogen in the low excited states necessary for an independent determination of CPT violation and examination of various gravitational theories [recent CERN experiments]. A concomitant advance in large-scale time-dependent simulation techniques has greatly enhanced our capability to understand and control such phenomena.

[1] Y. Shin et. al. Phys. Rev. Lett. 92, 050405 (2004); L. Collins et. al. cod-mat/0404149.
[2] S. Mazevet et. al. Phys. Rev. Lett. 88, 055001 (2002).


November 16, 2004
3:00 pm (Tuesday)

Dr. Larry Weinstein
Old Dominion University

How Protons Pair: Nucleon Correlations in Nuclei

Inaugural Lecture

One of the fundamental questions in nuclear physics is how nucleons (protons and neutrons) combine to make nuclei. The simple shell model, where the individual nucleons interact with the average of all the other nucleons and are thus placed neatly into shells (s, p, d, ...), only describes about 60% of the nucleus. Nucleons are composite, strongly interacting objects. When two nucleons are at very short distances a) they overlap and b) they repel each other extremely strongly. Thus, these short range correlations are responsible for the high momentum part of the nuclear wave function. By studying these correlations, we can hope to learn about the behavior of nucleons at very high densities (ie: when they overlap).

This talk will survey our knowledge of nuclei, from studies of individual nucleon behavior to the latest measurements of short range correlated pairs.


November 30, 2004
3:00 pm (Tuesday)

Dr. Marianna Safronova
University of Delaware

Parity nonconservation in atoms: current status and remaining mysteries

Study of parity nonconservation (PNC) in heavy atoms provides atomic-physics tests of the electroweak Standard Model and led to a first measurement of the nuclear anapole moment. The PNC interaction leads to a non-zero amplitude for transitions otherwise forbidden by the parity selection rule, such as the 6s-7s transition in cesium. Combining experimental measurements and theoretical calculations of the PNC amplitude permits one to infer the value of the weak charge. In the first part of my talk, I will report on the current status of the calculation of the Cs PNC amplitude and its uncertainty and resulting value of the weak charge. The PNC experiment in Cs, combined with the calculation of the spin-dependent PNC amplitude, also yielded the value of the nuclear anapole moment and allowed the placement of constraints on PNC meson coupling constants which were found to be in disagreement with those obtained from other nuclear parity violating experiments. I will present preliminary results of the new calculation of spin-dependent amplitude in Cs conducted using a relativistic all-order method and discuss the issue of the accuracy of the atomic calculations needed to derive the value of the anapole moment. Finally, I will comment on the general status of parity nonconservation in other atoms and the search for a permanent atomic electric dipole moment.


December 7, 2004
3:00 pm (Tuesday)

Dr. Chris Greene
University of Colorado

Making Molecules and Other Strange Animals in the Ultracold

This talk will consider one of the most exciting directions being pursued in current Bose and Fermi gases, namely the use of controllable Feshbach resonances to convert a gas of atoms into molecules. I will discuss related phenomena and review some of the recent theoretical and experimental progress, and show how the ultracold environment leads to the possibility of forming a new and highly unusual class of diatomic molecules.