Research Projects
The projects and groups listed below are intended to provide interested students with an overview of research offerings in the Department of Physics, University of Washington. The list is not inclusive, but it is representative of the breadth of research opportunities within the Physics Department and INT. Students with particular interests should feel free to ask Wick or Martin whether special projects can be designed: we have done this in past years with good success.
NUCLEAR PHYSICS LABORATORY
The Rate for 7Be Solar Neutrino Production
Faculty: Kurt Snover, Tom Steiger, Arnd Junghans, Eric Adelberger
The "solar neutrino puzzle," one of the current major puzzles in physics, consists of the observation that many fewer neutrinos from the sun are detected here on earth than are predicted by solar model calculations of the expected flux. We have recently developed the apparatus and techniques for a new measurement of the cross section (reaction rate) for the fusion of 7Be with low energy protons. This reaction rate is a crucial ingredient in the model calculations. The interested student will have an opportunity for a hands-on participation in all phases of the measurement and its interpretation.
Testing the Equivalence Principle using a High-Precision Torsion Balance
Faculty: Eric Adelberger, Stefan Baessler, Jens Gundlach, Blayne Heckel
The Eot-Wash group is building a new instrument to make the world's most precise test of Einstein's equivalence principle which says that gravitation is equivalent to an acceleration of the coordinate frame and is the underpinning of general relativity. You can find out more about this by clicking on the Eot-Wash research group on the University of Washington Physics Department home page on the Web. We have several interesting technical projects suitable for experimentally inclined summer students. Our lab is well equipped with instrumentation, machine and electronic shops so that plenty of resources are available for attacking these problems. Two examples are:
1) developing a higher performance optical system for reading out the twist of the torsion balance
2) developing an actively controlled temperature-regulation system for the torsion balance. We currently hold the temperature constant to a few millidegrees and want to do better.
Measuring the Gravitational Coupling Constant G
Faculty: Jens Gunlach, Eric Adelberger, Blayne Heckel
The gravitational constant (Newtons constant) is one of the most fundamental constants in nature. Surprisingly its value is still relatively poorly known and has recently been subject to some controversy. We have developed a new method to measure this constant accurately and are now building the apparatus. Possible projects for an REU student range from numerical simulations to designing and building of the actual hardware. Check out http://mist.npl.washington.edu/eotwash.
Weak Interactions, Symmetries, and Neutrinos
Faculty: Steve Elliott, Hamish Robertson, Tom Steiger, John Wilkerson
Our group is involved in a number of projects on the weak interaction and neutrinos. These include emiT, a precision neutron beta decay measurement that is testing time-reversal invariance, analysis of data from the SAGE gallium solar neutrino experiment (an experiment sensitive to the low-energy p-p fusion neutrinos), and measurements and analysis of a new exploratory experiment on the detection of cosmic-rays in the radio-frequency spectrum. We are also investigating an idea for using Pb as a target in a new neutrino-oscillation search at an accelerator, as Pb has a relatively large cross section for neutrino interactions. An REU student is encouraged to consider working with us in any of these areas.
The Sudbury Neutrino Observatory
Faculty: Peter Doe, Steve Elliott, Hamish Robertson, Tom Steiger, John Wilkerson
The Sudbury Neutrino Observatory (SNO) is a massive, heavy water Cerenkov detector located 2 km underground in Sudbury, Ontario. Data-taking with the detector full of heavy water is expected to begin in spring 1999. The experiment is aimed at trying to resolve the "solar neutrino problem", namely that experiments see fewer neutrinos from the sun than predicted by theory, and also that an explanation of the problem seems to require new neutrino properties such as mass and violation of lepton family number. Work at UW in the summer of 1999 by our SNO experimental group (5 Faculty, 1 postdoctoral fellow, 6 graduate students) will include the first use of the SNO primary data acquisition system, the construction of a neutron detector system that will be used in SNO to make the key measurement of neutral-current neutrino interactions and the testing of the remote deployment hardware for these detectors.
The Washington Large Area Time Coincidence Array
Faculty: John Cramer, Peter Doe, Steve Elliott, John Wilkerson, Jeff Wilkes
We propose to construct the Washington Large Area Time Coincidence Array (WALTA), an extended network of cosmic ray shower detectors, the elements of which will be placed in Washington area high schools. The primary functions of this network are physics education outreach and investigation of ultra high energy cosmic rays, the existence of which is one of the major unsolved problems of contemporary astrophysics. Work at UW in the summer of 1999 will include computer simulation of the response of the array to ultra high energy cosmic rays, prototyping an individual array element and characterizing its response to cosmic rays. An REU student would be a welcome participant in any of these activities.
GEOPHYSICS
The Physics of Lightning
Faculty: Marcia Baker, Brian Swanson
Large drops (500 microns to millimeters in size) are necessary for lightning initiation. We suspect they shatter as they freeze and that the fragments play important roles in charge transfer. We have designed and built a table top apparatus to study this phenomenon, which would serve as an excellent REU project.
Experiments and Theory in the Phase Behavior of Ice in Porous Media: Frost Heave
Faculty: Greg Dash, John Wettlaufer, Van Hodgkin
A primary motivation for understanding surface phase transitions in ice concerns the important roles they can play in a host of environmental problems ranging from polar stratospheric cloud chemistry to frost heave in porous media. The dramatic deformation of water saturated soils in cold climates is known generically as "frost heave." Yet it is rather more appropriate to refer to frost heave as the collective action of a number of phenomena each of interest and intense study in its own right. Although frost heave is clearly not caused by the volume expansion of water during solidification, for many years it has been known to be associated with the existence of stable liquid water at subfreezing interfaces. However, the varied causes of this water have obscured attempts to extract the fundamental mechanisms driving frost heave. In a porous medium, curvature, confinement, interfacial roughness and disorder, impurities and interfacial premelting all contribute to the finite volume fraction of water at subfreezing temperatures. Individually, these effects have distinct temperature dependencies, but their combined effects have thus far limited frost heave research to semi-empirical treatments. It is for this reason that we have focused on isolating the role of interfacial melting in the existence and mobility of unfrozen interfacial water. The intermolecular origin of the films, the effect of external forcing and the geometry of the confining wall are the main features of our studies. A student would have an opportunity to engage in both experimental and theoretical work. The table top experiments center around an optically thin chamber that allows visual, photographic and interferometric observation of ice growth and solute redistribution in their very early development. Theory involves local studies of thin film flow and continuum mechanical treatments of collective phenomena.
PHYSICS EDUCATION GROUP
Instructional Strategies for Teaching Physics
Faculty: Lillian C. McDermott, Paula Heron, Peter Shaffer, Stamatis Vokos
The Physics Education Group conducts research on student understanding of physics and uses the results of this research to guide the design of instructional materials. REU participants will have the opportunity to participate in programs shaped by the group's research, such as the summer program for K-12 teachers and the tutorials for the introductory physics course. In addition to taking part in classroom activities, previous REU participants assisted in investigations of the effect of different instructional strategies on student understanding of important fundamental concepts by analyzing student performance on qualitative questions before and after instruction.
EXPERIMENTAL PARTICLE PHYSICS
The Large Hadron Collider
Faculty: Henry Lubatti
The experimental particle physics group is preparing to participate in the next generation of experiments at the Large Hadron Collider, an accelerator under construction at CERN, Geneva. The summer project would involve the testing of components of a muon system for a detector to be constructed at the LHC. An REU student could be easily integrated into the measurements and evaluation. The required physics knowledge can be acquired from discussions with group members and from reading.
Neutrino Physics with SuperKamiokande and K2K
Faculty: Jeffrey Wilkes
Super-Kamiokande is a joint Japan-US collaboration operating the world's largest underground neutrino observatory. Neutrinos are subatomic particles which have no electrical charge, are very nearly massless, and interact only via the weak nuclear force. They are products of radioactive decay processes, and so are produced abundantly in our Sun, and in other astrophysical sources like supernovae and Active Galactic Nuclei (AGNs). Super-Kamiokande is located about 200 km northwest of Tokyo, and is a water cerenkov detector, which means it is a large (40 meters diameter by 40 meters tall) tank of ultra-pure water viewed by thousands of sensitive phototubes.
Super-Kamiokande addresses some of the most important open questions in physics today, such as: why does the Sun appear to produce only half as many neutrinos as theory would predict? Do neutrinos have mass? Do protons decay, as predicted by Grand Unification Theory?
Last June, Super-K was in the news as we published results which, for the first time, unambiguously demonstrated that neutrinos must have non-zero mass. This year, we began taking data using an artificial neutrino beam, directed from the KEK particle accelerator near Tokyo through 250 km of earth to Super-K. The K2K (KEK to Kamioka) experiment will give us a neutrino source with clearly defined properties, allowing careful refinement of Super-K atmospheric neutrino results. Next year, we will temporarily shut down Super-K to upgrade the detector hardware. The UW group plays a major role in all these activities.
One or two REU students are invited to join our staff and graduate students in working on hardware construction, data analysis and support software.
The Large Electron-Positron collider at CERN
Faculty: Steve Wasserbaech
Members of our group are conducting research in electron-positron collisions with the ALEPH detector. The experiment is located at the European Laboratory for Particle Physics (CERN) in Geneva, Switzerland. ALEPH is studying the electroweak interactions in a research program of unprecedented scope and precision. In 1998 the LEP collider achieved the world's highest e+e- collision energy (189 GeV). The energy is expected to be increased even higher in 1999, extending the sensitivity of our searches for the higgs boson and supersymmetric particles. REU students in our group will be based in Seattle and participate in a data analysis project.
COSMOLOGY
Dark Matter
Faculty: Chris Stubbs
We are engaged in a number of projects that address some of the most fundamental open questions in cosmology: 1) What is the nature and distribution of the dark matter that is the gravitationally dominant constituent of the Galaxy? 2) Will the expansion of the Universe continue forever, or will the Big Bang be followed by the big crunch?. We develop innovative instrumentation for astronomical observations, and in particular we make extensive use of the 3.5 meter diameter ARC telescope in New Mexico. One or more REU students would be welcome to join our group to help with our instrumentation efforts.
Cosmology and Large Scale Structure
Faculty: Tom Quinn, George Lake, Derek Richardson
Our knowledge of the largest structures in our Universe has grown dramatically in the past decade due to both both high quality observational surveys and theoretical simulations. Nevertheless, our understanding has been held back because of the difficulty in visualizing the complex three-dimensional structure. For example, a debate continues as to whether galaxies are found primarily on two-dimensional ``walls'', or one-dimensional ``filaments''. One REU student is invited to join our effort in analysis and visualization of observed and simulated galaxy catalogues.
CONDENSED MATTER EXPERIMENT
Low Temperature Behavior of Thin Films
Faculty: Oscar Vilches
The Low Temperature Physics laboratory is engaged in experiments to study, at low temperatures, the thermal properties of one to several layers thick films of hydrogen, deuterium, deuterium hydride, and the two stable isotopes of helium, 3He and 4He. For single layer films, leading questions are: a) to what extent it is possible to control the solidification temperature of the molecular hydrogen isotopes, b) phases and phase separation in 3He-4He mixtures, c) supercooling of hydrogen, and d) frost heave in hydrogen in porous media. Items (a) and (c) are related to the possibility that if molecular hydrogen films could be kept in the fluid state down to about 1K they will become superfluid. Experiments are done in the range of 1 to 10K. Item (b) has a very interesting counterpart in bulk mixtures, where isotopic phase separation is observed in both the solid and the liquid mixtures. Item (d) has a strong similarity to studies of frost heave in water/ice, with the added possibility that quantum quantum mechanical zero point motion plays a role. A project related to item d) is a study of frost heave in Ar, which was started by a 1998 REU student. We have been able to observe optically the formation of Ar lenses in a porous silica powder. This project will welcome a new REU student for Summer 1999. Additional individual projects may be possible, some related to measurements of the heat capacity of very small samples. Other projects, including working with a graduate student in an ongoing experiment, are possible.
Scanning Probe Microscopy
Faculty: Sam Fain
We are using contact mode atomic force microscopy to characterize the interface between nanometer sized probes and the surface of ice. In addition we are studying forces exerted on a surface in intermittent-contact mode atomic force microscopy. An undergraduate wishing to learn about atomic force microscopy could participate in either of these projects.
X-ray Phase Contrast Microtomgraphy
Faculty: Gerald Seidler
The advent of the third generation synchrotron x-ray sources has provided experimentalists with x-ray beams of unprecedented intensity and collimation. One technique especially enhanced by these new beam characteristics is microtomography, more commonly known as computerized axial tomography or CAT scans. In addition, there is a new alternative to traditional absorption tomography which may have several order of magnitude higher spatial resolution: phase-contrast tomography. Due to the high photon energy of hard x-rays (several keV and higher), the photon frequency is well past any plasmon frequency for condensed matter and consequently the dielectric constant is less than one, usually by about 10^-3 to 10^-4. Although a small effect, the high beam collimation readily allows observation of x-ray refraction effects. The question is, how does one uniquely invert multi-angle information about x-ray refraction to obtain the mass distribution of the object being studied? Even with an incomplete answer to this question, research groups in Europe have been able to perform 100nm resolution tomography of simple objects, such as a mosquito's knee and a spider's fang. The student on this project will work on the general question of the inversion of phase-contrast data. This will include theory, modeling, and data analysis.
ATOMIC PHYSICS
Atomic Tests of Parity Nonconservation and Time Reversal Symmetry
Faculty: Norval Fortson, Blayne Heckel, Michael Romalis
Students will be able to work directly on small scale atomic physics experiments that probe the elementary particle physics frontier. In one experiment, the electroweak force between electrons and quarks inside atoms is measured by the small degree of left-right asymmetry displayed by these atoms. In another, a permanent electric dipole of an atom is being looked for as evidence of forces that distinguish between forward and backward in time. In both kinds of experiments, students can use and develop high precision lasers and other tools of modern atomic physics.
Precision Measurements on Single Trapped, Laser-Cooled ions
Faculty: Hans Dehmelt, Justin Torgerson, Warren Nagourney
We work entirely with single atomic ions at rest in space. The ions are stored for long periods (up to a month) in an electrodynamic ion trap and are brought to rest using the radiation pressure of a laser beam. By studying essentially motionless ions in such pristine isolation, extremely precise measurements can be made. One application being vigorously pursued is the construction of a single-ion optical frequency standard. An atomic clock based upon such a standard could have an accuracy of one part in 10^18 (or about one second in the lifetime of the universe). REU students can help with the myriad mechanical, optical and electronic tasks needed to bring these experiments to fruition. Since certain single ions can be seen with the slightly aided human eye (aided by a simple microscope), the interested student can experience an intimate connection with atomic matter not available in most other disciplines.
Penning Trap Mass Measurements
Faculty: Robert Van Dyck, Jr., Paul B. Schwinberg
The primary effort of this research program is the development of the UW-Penning trap mass spectrometer to the highest possible accuracy. Using rf methods for observing the normal mode frequencies of a single isolated ion, bound to a small electro-magnetic cage called the Penning trap, it has become possible to measure masses of low mass-to-charge ions relative to an appropriate calibration ion with a precision that now exceeds one part in 10-billion.
Our immediate goal is the continued development of a high precision and high accuracy mass spectrometer with the added capability of external loading of ions. One possible application of such a spectrometer is an experiment that will yield an independent determination of the fine-structure constant. We are presently in the process of upgrading the front-end amplifiers for these Penning traps (i.e. the stage that does the actual particle detection). Any interested REU student can help characterize the latest generation of GaAs FETs for cryogenic operation.
Measurements of the Electron and Positron g-factors
Faculty: Hans Demelt, Paul Schwinberg, Robert Van Dyck, Jr.
We are engaged in an effort to further improve our measurements of the electron and positron g-factors, which have provided a very precise test of quantum electrodynamics of unprecedented accuracy. Our immediate goal here is to re-evaluate that experiment in hopes of developing/characterizing more efficient methods of loading, centering and/or transferring positrons within our traps. The interested REU student will have hands-on participation in this project.
RESEARCH IN THE PHYSICS OF MUSIC
Faculty: Vladimir Chaloupka
Physics of Music investigates the production, propagation and perception of musical sound. Some current projects include room acoustics studies using the modern "minimally intrusive" techniques, physics of consonance/dissonance, experiments on the absolute pitch perception, and measurement and evaluation of the pipe organ sound, with emphasis on the role of physical imperfections necessary to achieve the perception of perfection. Simulations are performed using advanced MIDI techniques. In addition to Physics, these projects touch on Computer Science, Electrical and Mechanical Engineering, Hearing Research, and of course Music. Many aspects of this research are well suited for the participation of undergraduate students.
THEORY
Numerical Methods for the Time-Dependent Local-Density Approximation
Faculty: George Bertsch
A powerful technique to model the electronic motion in atoms, molecules, and condensed matter is the time-dependent local-density approximation. The theory is limited by the computational methods, but so far they have not been optimized for this problem. The research is to make computer programs to try vary numerical techniques to improve the performance of the method. If we find methods that improve performance by a factor of 3-10, the reseach would not only be publishable but might lead to widespread adoption of the technique in the condensed matter community. The student must have experience in scientific programming and a concentration of course work in mathematics or mathematically oriented science (physics or engineering). Examples of the research in this area may be found on my web page, http://archive.int.washington.edu/users/bertsch/
Light Front Quantum Mechanics
Faculty: Jerry Miller
In 1947 Dirac introduced a new form of relativistic quantum mechanics in which the variable ct +z acts as a "time" coordinate and ct-z acts as a "space" coordinate. This so-called light front formalism was largely forgotten until the 1970's, when it turned out to be useful in analyzing a variety of high energy experiments. Despite the phenomenological success of this formalism, it has enjoyed only limited use in computing wave functions of particles and atomic nuclei. The present project is devoted to using the light front formalism to solve quantum mechanics problems involving bound and scattering states. A mathematically strong REU student would learn about relativistic quantum mechanics through the process of solving the relevant relativistic equations. This project would involve working on interesting and timely topics and could provide great preparation for graduate school quantum mechanics, field theory or even string theory.
Effective Field Theory in Nuclear Physics
Paulo Bedaque, Daniel Phillips, and Martin Savage
Effective field theories (EFTs) are based on the simple idea that details of the short-distance interactions of a system of particles should not strongly affect the low-energy properties of that system. They offer ways to systematically include information on the interactions between the particles at short range while making only minimal assumptions about this dynamics. Hence, EFTs have proven extremely useful in exploring the ways in which effects not included in the "standard model" of particle physics might manifest themselves in low-energy observables.
In recent years much effort has been invested in applying these ideas in nuclear physics. We know that the forces between neutrons and protons are very complicated at short distances, and yet we believe that these complications should be irrelevant for many nuclear physics phenomena. The University of Washington has been a leader in this work. Some of us have focused on applying effective field theory to a number of aspects of the physics of the neutron-proton system. Others have been involved with the issues which arise when one attempts to apply the ideas of effective field theory to a systems of three and four neutrons and protons. This REU project is an exciting opportunity for an undergraduate student to become involved in work which represents an innovative approach to nuclear physics. It would provide training in nuclear theory, quantum mechanics and field theory which would be good preparation for graduate school courses on these topics.