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Spring 2005

Schedule Spring 2005

January 11, 2005
3:00 pm (Tuesday)

Dr. Winston Roberts
Old Dominion University

The Quark Model of Hadrons, and the Pentaquark

Inaugural Lecture

After I introduce the known quarks and their properties, the concept of color, and the evidence for it are discussed. The application of isospin to up and down quarks, and the extension to include strange quarks is presented, along with the expected multiplets of hadrons. The motivations behind more explicit quark models are briefly outlined, and the results of work within the framework of such a model are presented. The relationship of this work to Jefferson Lab, and to recent evidence for a pentaquark state, are also discussed.

January 18, 2005
3:00 pm (Tuesday)

Dr. Thomas F Gallagher
University of Virginia

Non dispersing Wavepackets

Schrodinger proposed that the motion of the localized probability density of a quantum wavepacket could mimic the motion of a classical particle. Mode locked lasers have allowed the creation of wavepackets, and wavepackets of highly exited, or Rydberg, atoms have been made and studied extensively. However, due to the dispersion in the energy level spacings and technical dephasing, the localization of the wavepacket disappears in tens of orbits. Adding a small microwave field at the orbital frequency phase locks the electrons' motion, and wavepackets lasting 15,000 orbits have been observed. In addition, the phase lock between the electron motion and the microwave field allows us to alter the orbital frequency by chirping the microwave frequency.

January 25, 2005
3:00 pm (Tuesday)

Dr. C. Lew Cocke
J.R.Macdonald Laboratory, Physics Department, Kansas State University

Photon-ion Collisions and Molecular Clocks

The timing of molecular rearrangements can be followed in the time domain on a femtosecond scale by using momentum imaging techniques. Three examples will be discussed: First, the diffraction of electrons ejected from the k-shell of one of atomic constituents of the molecule takes a "picture" of the molecule, and the correlation between the momentum vector of the photoelectron and the subsequent fragmentation pattern is used to estimate the time delay which accompanies the latter process. Second, the kinetic energy release of proton pairs from the double ionization of hydrogen by fast laser pulses is timed using the 2.7 fs optical cycle as a clock. The mechanisms of rescattering, sequential and enhanced ionization are clearly identified in the momentum spectra. Pump probe experiments allow us to follow the simultaneous propagation of coherently launched wave packets in different exit channels. Third, the operation of rescattering double ionization in the case of nitrogen and oxygen molecules will be discussed. The use of rescattering to probe the structure of the outer orbitals in molecules will be demonstrated.

February 8, 2005
3:00 pm (Tuesday)

Dr. John E. Thomas
Duke University

Optically-Trapped, Strongly-Interacting Fermi Gases

Strongly interacting Fermi gases provide a paradigm for strong interactions in nature and impact theories in several disciplines, including materials science and condensed matter physics (high-temperature superconductivity), nuclear physics universal interactions, quark-gluon plasma), high-energy physics (effective theories of strong interactions), and astrophysics (compact stellar objects). The common feature which all of these systems share is that spin-up and spin down particles ``strongly" interact, i.e., the zero-energy scattering length far exceeds the interparticle spacing.

We use all-optical trapping methods to produce a highly degenerate, spin-up/spin-down mixture of fermionic 6-Li atoms at a temperature of <50 nK. An applied magnetic field (840 G) tunes the system to a collisional resonance where strong interactions are produced. I will describe our observations of novel hydrodynamic expansion, which simulates a quark-gluon plasma, our studies of collective modes which provide evidence for high-temperature superfluidity, and our recent measurements of universal thermodynamics, which test predictions for nuclear matter.

February 15, 2005
3:00 pm (Tuesday)

Dr. Geoffrey Krafft
Jefferson Laboratory

Energy Recovered Linacs, Short Pulses of X-rays, and Pulsed Beam Thomson Scattering

A longstanding scientific wish has been for an ability to acquire time-resolved information about the structure of molecules. Having such an ability could eventually lead to making short time-scale movies of important molecular reactions. Synchrotron radiation sources, which provide photons up to 100 keV energy, are ideally suited to performing measurements of structure, but are unfortunately limited in the minimum time duration of their emitted photon pulses to about 10 psec by the length of the electron pulse stored in the ring. Recently, serious work has begun on Energy Recovered Linac radiation sources, which may prove to allow time resolved X-ray structure studies on the 10-100 fsec scale.

In this talk I will review work at Jefferson Lab, in collaboration with Cornell University, on designing such a source and the work done creating a short pulse X-ray source at the Free Electron Laser at Jefferson Lab. Table Top TeraWatt Lasers, which deliver very high laser energies in very short pulses, are the mainstay in short time scale (<100 fsec) studies of a wide variety. The intensity in such lasers is high enough that the wide variety of nonlinear phenomena, e.g. radiation red shifting and harmonic generation, become prominent in the radiation spectra. In this talk a solution to the problem of pulsed beam Thomson Scattering is presented and used to analyze experimentally interesting scattering geometries. For off-axis Thomson scattering, strong dipole emission at the second harmonic occurs, oriented along the direction of laser incidence, and angular asymmetries in the frequency of emission arise. All of these effects can be computed exactly within the far-field limit by a fairly simple procedure.

February 22, 2005
3:00 pm (Tuesday)

Dr. Wesley Colley
Old Dominion University

Gravitational Lenses in Cosmology

Einstein once imagined using the relativistic deflection of light by massive objects to create telescopes with galactic focal lengths; a star would be the "objective lens," and our telescopes would function as the eyepieces. However, because the deflections are so tiny, the idea was abandoned. Only when a much different lensing system was discovered accidentally--in this case an entire galaxy lensing a distant quasar--did we return to Einstein's idea. Since then, we have effectively used massive clusters of galaxies as a means to magnify background objects significantly. The strange optical properties of these lenses require careful modeling of the lens system, which in turn forms a direct measurement of mass halfway across the Universe, and constrains the matter density of the Universe. Gravitational lenses also introduce a time-delay along different paths, so that lensed variable objects, such as quasars, provide a direct measurement of the Hubble constant. These quasar systems have also exhibited a bizarre "flickering" that may be giving us clues as to the nature of dark matter.

March 1, 2005
3:00 pm (Tuesday)

Dr. Wolfgang Lorenzon
University of Michigan - Ann Arbor

Shedding Light on Dark Energy with the SuperNova/Acceleration Probe (SNAP)

Recent measurements have made the startling discovery that the expansion of the universe is accelerating. This result is based on the Hubble diagram for type Ia supernovae, and has been corroborated by results from several experiments. Einstein's General Theory of Relativity requires that some mechanism must drive this expansion rate either through a new form of energy, such as a new vacuum energy density (cosmological constant), or a yet unknown kind of particle or field fundamental to the creation and formation of the universe. The source of this acceleration is more powerful than the gravitation from all seen and unseen forms of matter and known energy. Theorists are unable to explain the observed effect and follow-up measurements would have a tremendous impact on the field of fundamental physics. The Supernova / Acceleration Probe (SNAP) Mission is expected to provide an understanding of the mechanism driving the acceleration of the universe. The satellite observatory is capable of measuring up to 2,000 distant supernovae each year of the three-year mission lifetime. These measurements will map out in detail the expansion rate of the universe at epochs varying from the present to 10 billion years in the past. SNAP will determine the spatial curvature of the universe, and measure key cosmological parameters. This sensitive experiment uses type Ia supernovae as an astronomical standard candle to provide a distance scale, which, combined with the redshift obtained from the spectral lines from the supernova and its host galaxy determine the cosmological parameters and ultimately the nature of the "missing energy" in the universe.

March 15, 2005
12:30 pm (Tuesday)

Note unusual time

Dr. Kathy Perkins
University of Colorado

A workshop on using PhET simulations in your physics course

Special Workshop

The Physics Education Technology project (PhET) has created and tested a large number of sophisticated interactive simulations for teaching physics. These can be run online or local copies can be downloaded, all for free (phet.colorado.edu). In this workshop, we will work with these simulations and discuss how they can be used effectively in lecture, lab, and as part of homework assignments to improve both student learning and engagement.

March 15, 2005
3:00 pm (Tuesday)

Dr. Kathy Perkins
University of Colorado

Using the tools of physics to teach physics

Much of the rapid progress of modern science comes from its solid foundation on objective quantitative data, the rapid widespread dissemination and duplication of ideas, results, and successful approaches, and the rapid utilization of technological developments to achieve new capabilities. However, scientists often abandon these powerful tools in their approach to the teaching of science. Choices of content and presentation in teaching are usually based on tradition, time constraints, and the subjective judgments of the instructor. This seminar will detail an alternative approach to teaching physics that mirrors the approach to successful research in experimental physics, and includes: collecting and utilizing valid quantitative data (both one's own and those from the research of others), using quantitative statistical analysis to extract information from experiments involving imperfectly controlled degrees of freedom, and taking advantage of useful new technology. The discussion will focus on using this approach to improve teaching practices and will include specifics from our work on developing and using interactive simulations to facilitate conceptual understanding and on measuring student beliefs about physics.

March 22, 2005
3:00 pm (Tuesday)

Dr. Fleming Crim
University of Wisconsin - Madison

Using Lasers to Explore and Control Chemical Reactions

Vibrational energy plays a crucial role in chemical reactions since the relative motion of the constituent atoms transforms molecules from reactants into products. Thus, one means of controlling the course of a reaction is selective excitation of vibrations containing a significant component of motion along the reaction coordinate. Experiments on both bimolecular reaction and photodissociation of vibrationally excited molecules demonstrate this possibility by selectively breaking chemical bonds. For example, it is possible to control which bond breaks in the reaction of Cl with CH3D and even to determine the relative reactivity of different vibrations that involve similar nuclear motions. These measurements raise the possibility of similar manipulations in liquids. Experiments using ultrashort laser pulses to prepare a bond vibration and to monitor the vibrationally excited molecule directly observe the flow of vibrational energy in isolated molecules and in molecules in solution. The rates of these processes determine the characteristic times for control of bimolecular reaction or photodissociation in liquids.

April 5, 2005
3:00 pm (Tuesday)

Dr. Mark G Raizen
Center for Nonlinear Dynamics and Department of Physics, The University of Texas at Austin

Experiments with a "Particle in a Box": Bose Einstein Condensates, and Maxwell's Demon

The "particle in a box" is at the heart of quantum mechanics and is a paradigm for many problems in physics. In this talk, I will describe recent experiments conducted by my group which confine a Bose-Einstein condensate to a one-dimensional optical box. These conditions should enable the experimental realization of a "quantum tweezer" for atoms and allow preparation of atomic number states. More generally, we have demonstrated the capability to measure atom statistics by single-atom counting, paving the way for the new field of quantum atom optics.

The concept of a "particle in a box" is also widely used in thermodynamics. The historic paradox of Maxwell's demon suggested a way to cause particles to accumulate in one side of the box, in an apparent violation of the Second Law. Motivated by these ideas we have developed a method to form an optical "one-way" barrier for atoms. This device would allow atoms coming from one side of the barrier to pass through, but those coming from the other side to be reflected. I will show how this idea can be used for phase space compression and cooling, as an optical realization of Maxwell's demon.

April 19, 2005
3:00 pm (Tuesday)

Dr. Bela Sulik
Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), Debrecen, Hungary

Ionization of Li atoms and H2 molecules by fast heavy ions: Analogies between photon and charged particle impact

In target-ionizing collisions of fast projectile ions, first order perturbation theories are often well applicable. In such cases, the momentum transfer can be formally considered as a "virtual" photon. This leads to a descriptive, simple model, which gives account different experimental findings. In the talk, I would like to show experimental data and their interpretation for two cases. For Li ionization two- and three-body effects can be separated in a good approximation, in analogy with the Compton-effect and the photo-effect. For the H2 molecule, a coherent emission from the two identical centers provides an interference pattern, which also can be well understood within the same framework.

April 26, 2005
3:00 pm (Tuesday)

Old Dominion University

Senior Thesis Presentations