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Physics
Faculty Research Summaries | Chairman 's Introduction
Isaac D. AbellaLaser Coherent Transients. Photon echo techniques are used to probe metastable excited states in rare gas mixtures such as helium, neon, and argon. The states are produced in a weakly ionized r.f. plasma discharge, and nitrogen-pumped dye lasers are used to generate the coherent super-position states. Spectroscopy of Rare-Earth Laser Material. Samples of YLF and YAG crystals doped with erbium, thulium, and holmium are being studied with selective laser excitation in the region of 780 nm, the erbium bands. These materials can be efficiently optically pumped by the AlGaAs-GaAs laser diode arrays, but we are using dye laser excitation. We are interested in the energy transfer process: Er to Tm, to Ho, which concentrates energy emission at 2.085 microns at room temperature and at liquid nitrogen. The process is a radiationless, almost resonant transfer of energy between sites and depends on the relative concentrations of the rare earth ions. In particular we are interested in measuring decay rates, excited state absorption, and branching ratios and detailed theories of such processes. Edward C. BlucherMy current research involves studies of CP violation in the neutral kaon system. The origin of CP violation, which is thought to be necessary for understanding the striking asymmetry in the abundance of matter and antimatter in the Universe, is one of the fundamental questions of particle physics. Professors Wah, Winstein, Winston, and I are working with physicists from twelve universities on an experiment (called KTeV) which was designed to be sensitive enough to observe a new form of this phenomenon. This experiment first collected data from October 1996 to September 1997. Based on an analysis of the first 20% of these data, our group recently announced that we had established the existence of a new form of CP violation, called direct CP violation. We are currently analyzing the full 1996-1997 data sample, and are preparing for another run in 1999. The additional data will allow us to make a precise measurement of this new type of CP violation. My previous work involved experimental studies of electroweak interactions with the ALEPH experiment at CERN's Large Electron Positron (LEP) collider. Sean M. CarrollI am interested in understanding the fundamental laws of physics and how they manifest themselves in the evolution of the universe. This somewhat extravagant ambition is cut down to manageable size by considering problems which lie at the interfaces of particle physics, field theory, cosmology, and general relativity. An example of such a problem is provided by recent observations of distant supernovae (as well as other data), which indicate that the expansion of the universe is accelerating rather than slowing down. If true, this is a profound discovery which poses a challenge to theories of particle physics and potentially to theories of quantum gravity. The acceleration can be explained by invoking a nonzero vacuum energy, or cosmological constant, but with a magnitude which seems implausible from a field-theory perspective. A variation on this idea is to introduce quintessence, a dynamical field which induces a vacuum energy which gradually decreases with time. I have studied some of the implications of this idea in the context of effective field theories, arguing that models based on approximate global symmetries are the most feasible among those proposed thus far, and suggesting an experimental test of such theories. I have also explored alternative proposals, including dark matter particles which gain mass as the universe expands, and modifications of general relativity which would only be noticeable on very large scales. Work on these possibilities is in progress. Some of my other current interests include unusual types of solitonic objects in field theories, including topological defects resembling the D-branes of fundamental string theory, and the origin of cosmological magnetic fields from phase transitions in the early universe. I plan in the near future to investigate the large-scale properties of inflationary universes, the holographic principle and black hole thermodynamics, and the role of supersymmetry in early-universe cosmology. Susan N. CoppersmithMy group investigates the interplay between disordered structure and dynamics in condensed matter systems, including granular materials, glasses, sliding charge density waves, and magnetic flux lattices in type-II superconductors. The aim is to understand the qualitatively new features which emerge because these systems are far from equilibrium. One major focus is understanding when and how disordered systems self-organize into states with unusual types of order. Another is trying to elucidate the nonlinear dynamics of quantum mechanical systems. Corbin E. CovaultI am particularly interested in the application of ground-based air shower detectors for gamma-ray astronomy. Our group has recently developed a new experiment, called STACEE (Solar Tower Atmospheric Cherenkov Effect Experiment). STACEE is currently operating at the National Solar Thermal Test Facility at Sandia National Laboratories in Albuquerque, NM. The Sandia site contains over 200 steerable heliostat mirrors, each with 36 square meters of collecting area. By taking advantage of these pre-existing mirrors, we have been able to develop a new experiment with a very large light collection capability. We use the heliostat mirrors at night to collect Cherenkov light emission associated with gamma-ray air showers. STACEE is sensitive to gamma-rays in the energy range from 50 to 250 GeV, corresponding to a previously "unopened window" between current space- and ground-based techniques. Observations in this window are key to understanding the mechanisms for high energy particle acceleration in some of the most powerful astrophysical sources, including pulsars, active galactic nuclei, and supernova remnants. Analysis of the first STACEE observations taken in late 1998 are currently underway with first results to be presented later this year. Albert V. CreweDevelopment of high resolution electron microscopes, particularly scanning microscopes. Theoretical and experimental electron optics. Design of magnetic lenses and electron guns. Current emphasis is on the correction of spherical and chromatic aberrations which are the limiting factors in all present high performance instruments. A new type of corrector using magnetically focused electrostatic mirrors is now being tested, and the theory is being extended to full scale high performance systems. In addition we are exploring new concepts which will extend high resolution microscopy into the low energy arena (<1,000 volts). James W. CroninJames Cronin and University of Leeds professor Alan Watson lead an international project to study the nature and origin of rare but extremely powerful, high-energy (>1019 eV), cosmic rays that periodically bombard Earth. The project includes more than 250 scientists from nineteen nations. The scientists will practice a new form of astronomy rooted in particle physics. Construction of the Pierre Auger Observatory, a giant detector array near the cities of Malargue and San Rafael in Argentina's Mendoza Province, will be completed by 2003, but researchers plan to begin observations as early as 2001. The site will contain 1600 particle detection stations 1.5 kilometers apart, arranged in a giant grid covering 3000 square kilometers, an area about the size of the state of Rhode Island. The Auger Project hopes later to construct a complementary northern hemisphere observatory which, together with the southern observatory, would allow studies of cosmic rays from the entire sky. Dean E. EastmanMy research interests include the development and application of leading edge synchrotron radiation techniques to interfaces, surfaces, thin films, and nanostructures relevant to future microelectronic devices and other novel material systems. Representative materials systems of interest include those relevant to (1) future Si CMOS-based technologies, (2) GaN and other III-V semiconductor films on Si and sapphire, and (3) multilayer magnetic thin film systems. Synchrotron radiation techniques address physical structures; e.g., nanostructures, surface and interface structures, stress/strain distributions, dislocations, defects and doping distributions, as well as chemical and electronic properties. These techniques include various X-ray diffraction, microspectroscopy, microscopy, and other scattering techniques. Various types of photoelectron spectroscopy techniques (including band-mapping) using synchroton radiation are used to study the electronic structure of surfaces, nanostructures, and solids. In addition to synchrotron radiation techniques, atomic scanning microscopy (STM, scanning tunneling microscope, and AFM, atomic force microscope) and STEM and SEM electron microscopy techniques offer powerful complemental capabilities to study physical and electronic structures. This research utilizes leading edge synchroton radiation facilities (beamlines/end stations) at the Advanced Photon Source (APS), the Advanced Light Source (ALS) and others. It also involves collaborations with leading researchers in industry, at universities, and at government laboratories who provide samples, complementary characterization and processing capabilities as well as knowledge in addressing key questions and opportunities in advancing the state of the art. These advanced sample preparation and processing capabilities also facilitate studies of novel mesophysics phenomena involving nanostructures. Ugo FanoBasic studies of atom-molecular dynamics. This project aims at describing and predicting the correlations and energy exchanges of electrons and nuclei in atomic and molecular processes. Experimental evidence leads us to formulate appropriate multiparticle non-separable wave equations whose study keeps introducing new approaches of very general significance. Peter G.O. FreundFrom my work on the number-theoretic features of string theory connected with the algebraic geometry of the strings' world-sheets, I have been led to the study of certain two-dimensional integrable models which exhibit similar number-theoretic features. This has yielded new results on scattering processes in two-dimensional integrable quantum field theories. It has long been known that in such theories there is no particle production and the scattering of two particles determines the scattering of three or more particles. In a very large class of such theories, it turns out that even the input two-particle scattering is determined by simple considerations of quantum-geometry. Geometries involving direct products of 4-dimensional anti-de Sitter (AdS) space with a 7-dimensional compact Einstein manifold, and of 7-dimensional AdS space with a 4-dimensional compact Einstein manifold which have appeared in the context of solutions of 11-dimensional supergravity found with M. Rubin, have recently been connected by Maldacena with conformal field theory in 3 and 6 dimensions. For certain cases this connection (and similar connections in other dimensions) have been studied in quite some detail by many authors. I am considering certain solutions of this type involving minimal supersymmetry or no supersymmetry at all. We have constructed gravitational analogs of Born's nonlinear electrodynamics. In a very different vein we studied the implications of discrete scale invariance in certain rupture phenomena such as stock market crashes. Henry J. FrischMy research is focused on the experimental exploration of new phenomena
at very high energies. The Tevatron at Fermilab is the world's highest
energy machine, with 3.6 ergs/collision. We are now upgrading the CDF
detector to be able to handle a factor of 20 more luminosity. More recently I have been exploring our data following hints of new physics. The general area I am interested in is final states with indications of two vector bosons (photon, W, Z) in them; the motivation is that if a pair of new particles with a new conserved (or partially conserved) quantum number is produced, they may each decay into a final state with a gauge boson (either real or virtual). The final states with two leptons were explored by M. Hohlmann in his thesis; the final states with two photons were explored by D. Toback in his recent thesis. At present we are completing searches in the photon+lepton channel; this will be the thesis of J. Berryhill. Two other searches involving photons are in progress: photon + missing energy which is the subject of the Senior thesis of D. Fernie, and photons with large observed energy (J. Berryhill). Our next data run is scheduled to begin in the fall of 1999. Our group is working on the Level 1 calorimeter trigger, and a specialized processor that is designed to recognize b-quark decays by their displaced vertex in real time (the SVT project). It is a very good time for graduate students to join the group, as we are building the hardware to take the new data, and the timing is right for the analysis to be a thesis. The dilepton and diphoton channels will continue to be my main focus: with the new analysis tools we are developing on the Run I data, we should be able quickly to see if the hints of new physics in the present data are real or not. It will be an exciting time! Robert P. GerochMy research interests have been in three areas. The first is in the structure of the partial differential equations of physics. It turns out that there is a class of such equations (called first-order, quasilinear, hyperbolic systems) that, apparently, is sufficiently broad to encompass the descriptions of all (classical) physical systems. This class leads to a "universal" formulation of physical field theories. The second is the issue of describing quantum systems via Feynmann path integrals. There has been found a class of evolution operators for which such path integrals do exist, and this class of evolution operators, remarkably enough, includes candidates that are "close," in a suitable sense, to all bounded operators. Thus, this framework provides justification for the path-integral formulation of quantum mechanics. The third-an outgrowth of the second-involves the broad mathematical structure of measure and integration theory. It turns out that there is a framework for this subject-in which, for example, both the measures and the functions to be integrated are valued in abelian topological groups-sufficiently broad to encompass all physical applications of measure and integration, yet sufficiently narrow that the subject can be developed within this framework. David G. GrierMy group is interested in understanding the mechanisms through which microscopic processes give rise to macroscopic properties in condensed matter systems. In particular, we have been studying structural phase transitions in two classes of model systems: colloidal suspensions and flux lattices in Type-II superconductors. Both of these systems consist of discrete "particles" which interact with each other and whose interactions lead to complex collective behavior. In the first case, the particles are polymer microspheres dispersed in a fluid solvent. In the second, they are individual quanta of magnetic flux piercing a superconductor. We have developed new techniques for measuring the tiny interactions between these particles while simultaneously imaging their collective behavior. Such detailed information usually is not available for conventional atomic materials undergoing phase transitions since the constituent atoms are small and rapidly moving. In this sense, our systems are "models" for studying general processes in condensed matter physics. Using our new techniques, we have discovered conditions under which microspheres carrying the same sign charge actually attract each other. This surprising result runs counter to fundamental assumptions in the study of complex fluids and helps to explain some previously mysterious collective behavior in colloidal suspensions. The same techniques should be useful in the near future for measuring interactions between polymers and proteins tethered to the surfaces of microspheres. An equivalent approach recently has led us to the first measurement of the vortex-vortex pair potential in a Type-II superconductor. We use direct imaging techniques to track the motions of the "particles" in our model systems and thus to follow the progress of phase transitions. Recently completed studies have focused on the freezing of supercooled fluids, melting of metastable superheated solids, and phonon-driven martensitic transitions in confined systems. Emphasis in the near future will be placed on phase transitions in two-dimensional and reduced-dimensional systems including flux arrays and colloidal monolayers. Experimental methods used in this work include precision digital video microscopy, optical trapping, optical interferometry, torque magnetometry and Bitter decoration. We also have begun to exploit the sponta-neously ordered crystals formed by the microspheres for their beautiful and potentially useful optical properties. Philippe Guyot-SionnestJeffrey HarveyMuch of the success of particle physics is based on situations where there is a small parameter (such as the fine structure constant in QED) and quantities of physical interest can be expanded in a perturbative series in terms of this small parameter. However there are many interesting problems for which this is not the case. These include confinement and chiral symmetry breaking in QCD and probably the questions of supersymmetry breaking and the choice of vacuum in string theory. There has been recent progress in these "non-perturbative" problems by using ideas based on supersymmetry and duality. Duality often allows one to reformulate non-perturbative questions in terms of a dual, weakly coupled description in terms of dual variables. In gauge theory the dual degrees of freedom are magnetic monopoles. In string theory the dual degrees of freedom are various types of solitonic extended objects (strings, membranes, etc.). Most of my work is focused on understanding duality and its applications both in field theory and in string theory. Particular topics I am currently studying include non-perturbative mechanisms for vacuum selection in string theory, the algebraic structure of BPS states in string theory, the role of anomalies in understanding the structure of extended objects, and the structure of black holes in string theory. Walter F. HenningStudies of nuclear structure at the limits of nuclear stability using heavy-ion beams from the ATLAS superconducting accelerator at Argonne National Laboratory. Search for the heaviest elements. Nuclear reactions of explosive nucleosynthesis and of interest to nuclear astrophysics, involving beams of short-lived nuclei. Studies of dense, hot nuclear matter in collisions between relativistic heavy nuclei; particle propagation properties in nuclei and in nuclear matter. Accelerator mass spectrometry for ultrasensitive radioistope detection and tracing applications; new particle detectors including low-temperature bolometers. Roger H. HildebrandDuring the last year our observations with the University of Chicago polarimeter, Hertz, at the Caltech Submillimeter Observatory have led to a wholly unexpected discovery. The surprise appeared when we compared the results of these observations at a wavelength of 350 microns with results obtained at 60 microns and 100 microns with our earlier polarimeter, Stokes, on the Kuiper Airborne Observatory. Contrary to all predictions we found that the degree of polarization often depends strongly on the wavelength, in some cases rising steeply and in others falling. An analysis of the results indicates that in regions where the spectrum falls, typically in the envelopes of molecular clouds, the cloud medium must be heterogeneous. There must be warm domains containing aligned dust grains and cool domains containing unaligned grains. We speculate that low mass embedded stars may be responsible for the heterogeneous structure. Radiation from the stars may heat nearby material and also spin up the grains to suprathermal velocities thus enabling them to become aligned with the ambient magnetic fields. This picture supports a theory by Draine and Weingartner concerning sustained radiation torques on interstellar grains. It thus appears that measurements of the polarization spectrum point-by-point may reveal both the magnetic structure and the radiation structure of the clouds. The principles discovered in the course of this work have led us to make several predictions concerning the polarization spectra and thermal profiles in several astrophysical environments (e.g., a steeply rising spectrum in tenuous clouds). We are currently working on a conceptual design for a polarimeter for SOFIA, NASA's new airborne observatory to be commisioned within the next three years. This instrument will provide the only access to the polarization spectrum in the range 60 to 200 microns, the range in which we expect the most rapid dependence on wavelength. Also in the last year I have completed my work on the construction of an echelle spectrometer for the Apache Point Observatory. Don York took over responsibility for this instrument in December when we jointly obtained the first stellar spectra at the observatory. We expect to commission the echelle in the spring of this year. Christopher T. HillFew things are more ubiquitous than "mass." The origin of all masses of the known elementary particles is tied to a fundamental scale in nature which is known as the "weak scale." The weak scale was first introduced by Fermi roughly 65 years ago, and we understand today that it is associated with the symmetry breaking of the Standard Model (electroweak theory). The weak scale has a measured value of about 175 GeV. The dynamical origin of this physical scale may be connected to a new strong dynamics, in analogy to the strong interactions (which have a scale of order 100 MeV). Alternatively, it may be associated with the emergence of a new symmetry, i.e., supersymmetry, near this scale. The mechanism of electroweak symmetry breaking may be coupled intimately to the heavy mass scale of the top quark, which poses a unique set of problems in the context of either approach. Approaches to understanding this phenomenon include model building, incorporating the dynamical ideas that are particle physics analogues of superconductivity. The study of high-pT physics and the development of new signatures for the associated phenomena play a major role. Finally, the study of optimal accelerator based programs, such as the high luminosity TeV33 program at Fermilab, and the feasibility of a Muon Collider are important components to this effort. During 1998 I continued my research interest in strong dynamics and its possible connection to electroweak symmetry breaking. I coauthored a key paper with H. Georgi (Harvard), R. Chivukula (B.U.), and B. Dobrescu (Fermilab) on the top quark seesaw mechanism of electroweak symmetry breaking. I am continuing this line of inquiry, and am collaborating with Dobrescu on investigating string-inspired scenarios for the emergence of extra space-time dimensions at the TeV scale. Heinrich M. JaegerMesoscopic Physics. On size scales below typically one micrometer, metallic, superconducting, and semi-conducting structures display properties which differ fundamentally from behavior on larger scales. In this so-called mesoscopic regime, the quantum nature of electrons leads to a breakdown of classical predictions for electron transport and to novel behavior not present in the macroscopic limit. We are investigating electronic transport in normal metallic and superconducting mesoscopic structures such as ultrathin films and arrays of nanometer-sized islands. This research explores the roles of carrier confinement, quantum fluctuations, and disorder. We utilize experimental techniques such as cryogenic and high-magnetic field measurements, scanning probe and electron microscopy, and electron-beam lithography. One area of our current research focuses on the self-assembly of nanoscale structures using diblock copolymers. A second area utilizes microfabricated Hall probes to explore the dynamical behavior of superconducting vortices. Granular Materials. Piles of dry grains of sand display a variety of behaviors that are in many ways different from those of other substances. Typically matter is characterized as either gas, liquid, or solid. Granular materials cut across these predefined boundaries. An example is the transition from solid- to liquid-like behavior at the onset of particle flow and avalanching down the slope of a sandpile. We have been investigating experimentally the complex, non-linear dynamics of granular flow and find that the macroscopic behavior of granular materials has parallels in many microscopic phenomena including magnetic flux creep in superconductors, charge density waves, and relaxation in spin glasses. Most recently we have explored convection patterns and period-doubling instabilities in vibrated granular systems, the force fluctuations inside static packings, and the glassy settling behavior of granular matter. We use capacitive probes, high-speed video imaging, magnetic resonance imaging (MRI), and x-ray tomography (at the Advanced Photon Source) to probe the behavior of granular materials. Leo P. KadanoffWe work on non-linear systems using the techniques of statistical physics. More specifically, we are studying how turbulent, chaotic, and stochastic behavior arises in dynamical systems, particularly hydrodynamical and biological systems. For example, we have been extensively concerned with the development of simplified models for turbulence, with the nature of mathematical infinities in the flow of fluids and of bacteria, and with models of granular materials. We use both analytical and simulational methods and try to use experimental data whenever possible. Our basic goal is to understand the nature of the complex motion that can arise in even very simple systems. This work has applications to mathematics, astronomy, and chemical engineering. Woowon KangMy research centers on the study of quantum, cooperative phenomena in systems such as the fractional quantum Hall effect (FQHE), organic superconductivity and sonoluminescence. Questions of interest in the FQHE include novel phase transitions and excitations, and the role of electron-electron interactions in determining the ground state properties. Recent experiments have focused on the study of spin degree of freedom in the FQHE, and we have observed rather unusual magnetic ordering associated with the spin transitions. In organic superconductors, the nature of pairing interaction that gives rise to superconductivity and the synthesis of new superconductors are of current interest. Sonoluminescence represents a most singular energy conversion process by which sound energy applied to a bubble filled with gas is converted to photons. At the heart of sonoluminescence is some unknown electrodynamical process that is responsible for the light production. The study of electronic properties of sonoluminescence is expected to yield considerable insight into the inner workings of this most unusual phenomenon. The investigation of sonoluminescence in a magnetic field so far has revealed an intriguing dependence of experimental parameters on magnetic field. Motivated by these findings, additional experiments of sonoluminescence under very high magnetic fields are currently under progress. David KutasovThere are many fascinating relations between gauge and string theories. Gauge theories describe the low energy limit of string theories, and both classes of theories have been recently discovered to enjoy certain strong-weak coupling duality symmetries that allow one to learn a lot about their quantum behavior. Also, it is believed that strongly coupled gauge theories can be described by an as yet unknown string theory, the "QCD String." My work in recent years has focused on different aspects of the interface of gauge and string theories, such as the transition from confining to Coulomb phase in gauge theories, the phase structure of strongly coupled supersymmetric gauge theories, electric-magnetic strong-weak coupling duality in field and string theory, toy models of QCD strings, and the so called "AdS-CFT" duality. I have also been involved in attempts to understand the fundamental formulation of string theory and its unification with membranes and higher "p-branes." Kathryn LevinOur interest is primarily in theoretical studies of exotic superconducting and magnetic systems. We ask questions such as: What makes different materials superconducting? What is the nature of their superconductivity? Our recent work has focused almost exclusively on the newly discovered high temperature superconductors. These are among the most exciting and unusual materials ever to have been discovered in solid state physics. The individuals who made this discovery were awarded the Nobel Prize, roughly a year after the publication of their results. There is every reason to believe that these materials will impact on technology and on our everyday lives. Cellular phones are one obvious application which is being considered, along with new designs for magnetic resonance imaging machines. As theorists our job is to understand the fundamental nature of these superconductors and to try to come up with alternate materials which may be superconducting at even higher temperatures. Riccardo Levi-SettiA Scanning Ion Microprobe (UC-SIM) has been developed that performs Secondary Ion Mass Spectrometry (SIMS) imaging microanalysis of materials in the sub-100 nm range of lateral resolution. The mass analysis of the secondary ions is carried out with a high performance magnetic sector chemical mass spectrometer. This by now renowned instrument continues to find unique application in the study of advanced ceramics, in collaboration with DuPont scientists, and in a range of biological studies. The ability to detect isotopes is of extreme value in cytogenetics, allowing the distribution of labeled nucleosides to be mapped in human metaphase and Drosophila polytene chromosomes. In collaboration with scientists of the Department of Medicine of our University, investigations on the role of divalent cations in the scaffold structure of human metaphase chromosomes are in progress. Systematic studies of bone physiology continue also to be pursued in collaboration with researchers of the Department of Medicine of the University of Rochester, N.Y. Emil J. MartinecMy work aims at uncovering the structural foundation of string theory (now sometimes called M-theory), which attempts to unify the basic forces. The theoretical underpinnings of the subject are finally taking shape, due to the recent discovery of nonperturbative dualities between different descriptions of the theory. The spacetime manifold on which particles and waves propagate is being replaced by a more "stringy" notion of geometry at short distances and/or in strong fields. One issue of interest to me is how string theory incorporates black holes as quantum states. This problem has turned out to be a rather sensitive probe of the theory, and will likely lead us to new notions of space, time, and dynamics. Gene F. MazenkoOur group has been concerned with understanding the growth of order in unstable systems. The simplest example of such a system is a ferromagnet, initially disordered at some high temperature, then subjected to a rapid temperature quench to a temperature below its Curie temperature. The system is now in an environment where it wants to develop a spontaneous magnetization. However, in the absense of any symmetry breaking fields, the system does not know in which direction to order. Each local magnetic moment aligns with it neighbors and spontaneous local ordering occurs. There is then a competition between the orientations of different local regimes. This competition results in regions of frustration which are relieved by the formation of defects. Depending on the nature of the order parameter, these defects can be domain walls, vortices, monopoles, strings, disclinations, etc. Our work has centered on developing a theoretical approach which can answer questions like: At a time t after a quench, how many vortices are there per unit volume in a system? How many of these vortices decay via vortex-antivortex annihilation during a certain time period? What is the average speed of a vortex? This type of work has applications in cosmology, superconductivity, superfluids, liquid crystals, magnetism, and in the physics of fluids. Frank S. MerrittI am a member of the OPAL collaboration, which has been carrying out high-precision measurements of electroweak physics at the LEP e+e- accelerator. Measurements near the Z0 resonance (91.2 GeV) over a 5-year period have provided the most precise tests (<0.1%) of the Weinberg-Salam electroweak theory and other physics. The LEP energy has been substantially increased over the last few years, reaching 189 GeV in 1998. A further increase to ~196 GeV will occur in 1999. This has opened up a number of new research areas, including the most sensitive search for the Higgs boson, the high-precision measurement of the W-boson mass (~80.3 GeV) through W+W- pair-production events, and searches for supersymmetric particles and other new physics. Our group is now working on W-mass measurements, Higgs searches, other new-particle searches, precision measurements of the tau lepton, and heavy flavor physics. I am also a member of the Chicago/ATLAS group, now developing the hadron calorimeter to be used in the ATLAS experiment at CERN's Large Hadron Collider. This will be by far the highest-energy accelerator in the world, and will take us into new physics beyond the Standard Model: supersymmetric particles, technicolor, and/or unexplained new phenomena. The Chicago group is now beginning a major software effort, first focussed on analysis of calorimeter test-beam data, and then (in 1999-2000) on development of the analysis system and code for ATLAS data analysis. Stephan MeyerSee Department of Astronomy and Astrophysics Dietrich MüllerOur research is directed towards several areas of high energy astrophysics: Origin of high energy cosmic rays. Up to energies around 1015 eV, cosmic rays appear to be accelerated in galactic shock fronts driven by supernova explosions, while the origin of particles with still higher energies is not understood. Observational constraints on the details of the shock acceleration mechanism and on the various models proposed for the origin of particles at the highest energies must come from precise measurements of the elemental composition and energy spectra of the individual cosmic ray components. To this end, we use two different detectors for observations on high altitude balloons. One of these, developed jointly with Simon Swordy, uses the novel technique of ring-imaging Cherenkov counters to measure the particle energy with very high precision. This instrument has been successfully flown in 1991, 1996, and 1997. Another instrument uses transition radiation detectors to permit measurements in the presently unexplored energy region between 1014 and 1015 eV. This detector exhibits a large sensitive area of nearly 5 m2 and is based on a concept that we successfully applied in a space flight on the Space Shuttle in the 1980s. A first balloon flight of long duration, carrying the detector for two weeks all around the northern hemisphere, is planned for Summer 1999. Search for anti-particles in the cosmic rays. Positrons and anti-protons are the only antiparticle species detected thus far in the cosmic radiation. They are generated subsequent to nuclear interactions in interstellar space and therefore provide an interesting probe on the structure of the interstellar medium and on the propagation of particles through the galaxy. However, there might also be more exotic contributions to the observed intensities of these particles. These issues are studied with a balloon-borne detector system which includes a superconducting magnet spectrometer. This instrument has been successfully flown in 1994 and 1995 and has measured the flux of positrons and electrons over a wide energy range. At present a modified detector system for the observation of high-energy antiprotons awaits a balloon flight in Spring, 1999. This work is conducted jointly with Simon Swordy and collaborators at several other institutions. Development of detectors for particles and gamma-rays. Much of our work depends on the development of novel detectors suitable for high-altitude balloon exposure or space flight, including imaging Cherenkov counters and transition radiation detectors. For the future, light-weight detector arrays with very large area are being studied for flights on the space station. A new program of observations of high energy gamma rays from galactic sources like supernova remnants, or from extragalactic objects like Active Galactic Nuclei, is planned with an array of ground-based air-Cherenkov telescopes. The array will be built in Arizona in a collaboration with several other institutions (the VERITAS collaboration). Sidney R. NagelWe have been interested in the glass transition and have studied it with a variety of spectroscopic techniques. We have reported that there appears to be scaling behavior that allows the collapse of all our dielectric data for all samples and temperatures onto a single curve providing evidence for a diverging susceptibility at the glass transition. We have been studying the flow and dynamics of granular materials, such as sand. We have studied sound propagation, vibration-induced convection and size separation and compaction, force fluctuations, and shear flow in these materials. We have investigated the properties of moving liquid interfaces, including drops at the point of snapoff, the formation of electrosprays, and selective withdrawal. We have studied the process of ring formation that occurs when a solute is deposited in a stain at the edge of an evaporating drop. Yoichiro NambuFermion hierarchy problem. The masses of the six generations of quarks and leptons are spread over almost six orders of magnitude for the charged particles, and another six orders if the (not yet well known) neutrinos are included. The pattern of the masses and mixings show no precise regularity. In the highly successful Standard Model, they are mere phenomenological parameters. So far none of the existing theories based on various unified theories have been able to offer a satisfactory account of them. I regard the problem of mass as something that should be looked upon afresh and without prejudice. Specifically I have been trying (1) to uncover some unnoticed regularities in the masses and mixings which might serve as a clue to model building and (2) to search for a general dynamical mechanism for generating hierarchies. I have found one possible new and simple regularity for quarks, but I do not have a theory about it yet. Aharonov-Bohm media. This is a long-standing unsolved mathematical problem which has interested me for twenty years: the behavior of an electron in a medium filled with nonquantized magnetic fluxes. The motivation came from my speculation that it might serve as a model for such theoretical ideas as the quark confinement in a medium of monopoles. If the fluxes are all parallel, the problem reduces to that of solving the Schroedinger equation in two dimensions in the presence of magnetic charges. Only explicit solutions for a single flux had been known, and its extension to many fluxes has turned out to be a highly nontrivial mathematical problem. But recently I have succeeded in constructing the solutions. Two different types emerge. In one, both charges and fluxes have to be treated as dynamical objects. In the other, the fluxes are fixed objects and a magnetic field is present, but the solution has no zero-field limit. The effect of the fluxes in a magnetic field is to shift the Landau levels for some of the states and to leave the rest unchanged. As a consequence of a general feature of the solutions, a medium made up of many fluxes in free space acts like an anti-magnetic field and tends to expel the charge. These properties may have interesting experimental consequences. Hagedorn-Rumer phenomena. It is well known in hadron multiple production (according to the so-called Hagedorn fireball model) as well as in string theory that the density of states increases exponentially with energy and competes with the Boltzmann factor so that thermodynamic equilibrium cannot be maintained above a certain limiting temperature. I have been interested in this as part of my search for phenomena that defy thermodynamics. The entropy of the black hole is of a similar but more drastic nature, and has been the subject of intense study in string theory lately. In classical physics I have found two simple examples of exponential density of states. One is a particle in a logarithmic potential, which had already been pointed out by Y. Rumer in 1960. The other is a particle under gravity and placed in a vessel whose horizontal cross section grows exponentially upwards. It should be possible to do a desktop demonstration of the latter case (or variants of them) at room temperature with particles of atomic weight of the order of 107 (e.g., viruses and synthetic microspheres). Recently I have also learned of theoretical investigations by S. Berry, who finds exponential density of states (more precisely, of local potential minima) in atomic clusters. I suspect this is a rather general phenomenon which might eventually become relevant to biology and the black hole problem. Reinhard OehmeWe study quantum gauge field theories, supersymmetric theories and duality, and connections of these theories with D-brane configurations in string theory. The confinement of gluons and quarks is a fundamental problem in non-perturbative quantum chromodynamics. Some time ago, we have obtained results about the phase structure of gauge field theories on the basis of analyticity, the renormalization group and the BRST cohomology. We also applied our methods to supersymmetric theories. Now we find that, for SUSY theories, our conclusions agree with those obtained recently on the basis of duality, which can relate strong and weak coupling properties of the theory. These connections are being explored in greater detail. In contrast to duality, our methods are applicable to non-SUSY theories. As a general method of imposing restrictions on quantum field theories with several parameters, we have introduced a theory of reduction of couplings. This method is more general than the imposition of symmetries. It is based upon renormalization group methods and reparametrization. Our reduction theory is finding a wide range of applications, from supersymmetric theories and their duality properties to the gauge-Yukawa unification in supersymmetric grand unified theories and the calculation of quark masses and other quantities. A comprehensive article for Physics Reports is in preparation. There are interesting connections between certain results of the reduction method and consequences of superstring theories. These relationships are being studied. René A. OngI am currently working in the area of experimental high energy astrophysics, using cosmic rays and gamma-rays. Between 1992 and 1997 we operated the Chicago Air Shower Array (CASA), a very large array of scintillation counters in Dugway, Utah. This experiment has studied cosmic ray air showers at energies above 100 TeV (1014 eV) and searched for gamma-ray point sources at these energies. A variety of publications resulted from this work, including the search for gamma-rays from extragalactic sources (AGN and gamma-ray bursts), the study of diffuse gamma-ray emission from the Galactic plane, and a stringent limit on the isotropic diffuse flux of gamma-rays that could come from the cascade of 1020 eV cosmic ray protons on the 3K CMBR or from the decay of topological defects created in the early Universe. In 1996, we installed a new detector at CASA to measure the lateral distribution of Cherenkov light in air showers. This detector (BLANCA) consists of 133 wide-angle Cherenkov collectors spread out on a 30-meter grid. We have accumulated a substantial data set with BLANCA and are now in the process of determining the cosmic ray composition at the poorly understood region between 100 and 10,000 TeV. My future research will be largely focused on gamma-ray astronomy at energies between 10 MeV and 10 TeV. With Corbin Covault, our group at Chicago is leading an effort to build a new atmospheric Cherenkov telescope called STACEE. STACEE uses 64 large heliostat mirrors originally built for solar energy to reflect Cherenkov radiation to a central tower, where secondary mirrors and cameras are located. We are in the process of constructing the full STACEE instrument, which should be completed by early 2000. In 1998 and 1999, we made preliminary observations using a portion of the experiment. The STACEE project is located at Sandia National Laboratories, near Albuquerque, NM and is a collaboration of about fifteen scientists from five institutions in the U.S. and Canada. A major scientific goal of STACEE is the exploration of the energy range between 20 and 250 GeV, the detection of AGN blazars out to redshifts Z~1.5, and observations of spectral cut-offs in the blazar spectra which will indicate absorption by the Intergalactic Infrared (IIR) field. In addition to STACEE, I am working on two longer-term projects for gamma-ray astronomy. With Mark Oreglia, I have been working on the development of GLAST, a possible orbiting satellite gamma-ray detector. GLAST will use silicon strip detectors for tracking and a large calorimeter to measure gamma-ray energies. The GLAST mission is very much on track and the full instrument could be launched as early as 2005. With Simon Swordy and Dietrich Müller, I am working on the development of VERITAS, a new ground-based atmospheric Cherenkov telescope. VERITAS will consist of seven large 10-meter aperture telescopes on Mt. Hopkins in southern Arizona. VERITAS will have exceptional gamma-ray point source sensitivity above 100 GeV, and at energies below this it will be complementary to STACEE. The range of physics to be covered by VERITAS and GLAST include detection of many more gamma-ray blazars, and possibly more pulsars and supernova remnants. The instruments can also make sensitive searches for non-standard physics, including Supersymmetry (neutralino annihilation in the galactic halo), primordial black holes, relic neutrinos and heavy particles from the Big Bang, and possible quantum gravitational effects. Mark J. OregliaI am currently spending most of my time with photons. As a member of the OPAL experiment, I am working with students and postdoctoral fellows to find the Higgs Boson, both in its "minimal" conventional form, and in more exotic decays into photons. This work is carried out at the University and at the Large Electron Positron accelerator at the CERN laboratory in Geneva, Switzerland. The OPAL collaboration has been conducting precision tests of the electroweak theory, searching for new particles which could couple to electron-positron collisions, and studying properties of b- and c-quarks and tau leptons. Other new particles for which I am searching are supersymmetric particles and excited quarks. The LEP program will continue to take data until the end of 2000. In 1996, the energy was nearly doubled, and systematic energy increases in the coming years have rejuvenated searches for new particles and tests of Standard Model parameters which are possible now that LEP is producing W-pairs. As of this writing, the LEP center-of-mass energy is 192 GeV. Because there is a slight chance that OPAL will not discover the Higgs boson, I am also a member of the ATLAS Experiment (see Professor Pilcher's research description). Photons from the cosmos cover all energy ranges and can be unique signatures of high energy processes in astrophysical objects, such as collapsing massive objects and Active Galactic Nuclei. Photons have an advantage over charged particles in that they do not bend in the intergalactic magnetic fields, and therefore point back to their source. I am a member of the GLAST collaboration, which hopes to launch a new satellite instrument with state-of-the-art technologies in 2005. I am studying calorimeters for spaceborne mapping of gamma ray point sources in the energy range of 10 MeV-300 GeV, and development of a Gamma Ray Burst instrument to measure accurately the temporal and spectral profiles of these rather mysterious events wherein point objects release enormous amounts of energy in the form of photons, covering large energy ranges and with peculiar time profiles. James E. PilcherA group of us from Chicago is studying high energy electron-positron annihilations with the OPAL experiment at LEP. The work has involved precise measurements of the properties of the Z boson and several tests of the electroweak theory with accuracies at the level of 0.1%. These tests lead to a prediction of the mass of the Higgs boson, the origin of electroweak symmetry breaking. The LEP facility is now operating at a center-of-mass energy of close to 200 GeV. Our group is involved in measuring the mass of the W boson, which is an important parameter in the electroweak theory. The error of this measurement should be less than 50 MeV once all the data has been collected. We are also searching for direct production of the Higgs boson, particularly in final states involving tau leptons or photons. Our current lower limit on its mass is 93 GeV. Another study in progress is of W bosons decaying to final states involving charmed quarks. The LEP facility offers the first opportunity for the direct observation of hadronic decays of W bosons. The charmed final states will provide a measurement of the parameter Vcs. We are also involved in the preparation of the ATLAS experiment for the Large Hadron Collider (LHC) to be built at CERN. This facility will allow most of the possible mass range for the Higgs boson to be directly studied and will also allow important searches for supersymmetric states. We are preparing the detector's hadron calorimeter, which measures the energies and trajectories of quarks and gluons produced in the high energy collisons. Thomas F. RosenbaumAt temperatures near absolute zero, new collective phenomena become possible. The quantum mechanical nature of materials is highlighted at the low temperatures, leading to a different class of phase transitions and to states with unusual excitation spectra. I use dilution refrigerator techniques to explore quantum magnets and glasses with connections both to quantum phase transitions and to the encoding of information, metal-insulator transitions with choreographed charge and spin degrees of freedom, new magnetoresistive compounds, vortex creep and tunneling, and exotic superconductivity. MilliKelvin temperatures often are combined with symmetry-breaking fields, such as uniaxial stress, to help constrain theory on fundamental grounds. These disparate topics are united by the theme of the interplay of correlation effects and disorder, and the issue of how macroscopic order can emerge from microscopic disorder. Jonathan L. RosnerRecent experiments on W and Z bosons at Fermilab and CERN and some non-accelerator experiments (including measurements of parity violation in atoms) have permitted tests of the theory of electroweak interactions with unprecedented accuracy. Studies are in progress to determine how these experiments shed light on new physics in the mass range of 100 GeV to several TeV. A parallel line of investigation deals with the weak couplings of quarks to one another, as parametrized by the Cabibbo-Kobayashi-Maskawa matrix. Various ways of learning these couplings more precisely are being studied. A key role is played by experiments on decays of mesons containing the "bottom" or "beauty" quark. Proposals are made, based in part on present data, for ways to detect the violation of CP symmetry (the combination of charge and space inversion) in decays of these mesons. Central to these studies is the "top" quark, discovered in experiments at Fermilab. Knowledge of the top quark mass sheds valuable light on other parameters of the electroweak theory, including the mass of the Higgs boson and the nature of the quark couplings governing CP violation. Other topics being investigated include properties of systems involving one or more heavy quarks (charm, bottom, and top), the possibility that quarks and leptons have a composite structure, and the role of neutrino masses in a more general understanding of fermion masses and couplings. Rosner also has completed a small experiment to search for and study radio-frequency pulses accompanying cosmic ray air showers, and is currently analyzing the data. This work is intended as a prototype for a system at the proposed Auger Giant Air Shower Detector. Savdeep S. SethiIn order to answer basic questions about the nature of spacetime and gravity, we need a quantum theory of gravity. String theory remains the most promising candidate for such a theory. In addition, string theory naturally melds the strong and electroweak forces with gravity in a unified framework. For many years, it appeared that there were a number of distinct string theories. However, it has become clear in recent times that each of these distinct theories is a limit of a unique eleven-dimensional theory known as M theory. Uncovering the structure of M theory is likely to radically alter our notions of spacetime and gravity. My research centers on understanding various aspects of M theory, string theory and Yang-Mills theories. Among the topics that I am currently studying are the constraints imposed by supersymmetry on string theories and Yang-Mills theories, D-brane dynamics, and compactifications of M theory to three and four dimensions. Melvyn J. ShochetMy research is carried out with the CDF detector, which we built at Fermilab to study collisions between 1000 GeV protons and 1000 GeV antiprotons. With the large data samples we have accumulated, at a center-of-mass energy three times larger than any previously produced, we have been able to study the strong and electroweak interactions and search for new phenomena. These studies include measuring the production cross sections for energetic quark and gluon jets, photons, and W and Z bosons; making a precision measurement of the mass of the W boson; measuring the production and decay properties of mesons containing b quarks; and searching for objects that are not included in the Standard Model of the elementary particles and their interactions, such as supersymmetric particles, heavy gauge bosons, and leptoquarks. Our most important result is the discovery of the top quark and the measurement of its mass. The initial evidence for the top quark was presented in April 1994, with the confirmation of the discovery announced in March 1995. At a mass of 174±5 GeV, the top quark is by far the most massive of the elementary constituents of the universe. We are now building a new CDF detector which will take data early in 2000 using the upgraded Fermilab Tevatron accelerator. We will collect two orders of magnitude more data than before, which will greatly improve our measurement of the properties of the top quark and our sensitivity to new phenomena. In Chicago we are designing electronic systems for selecting in real time the most important 300 collisions out of the 10,000,000 that will occur each second. This is an ideal time for new students to join our effort, since they will be able to participate in all stages of the experiment-building and testing the apparatus, commissioning the entire detector, data taking, and analyzing the high sensitivity data sample. John A. SimpsonOur experimental and theoretical research is focused on determining the origin and acceleration mechanisms of nuclear matter on all astrophysical scales extending from planetary magnetospheres (e.g., Mercury, Jupiter, and Saturn) to the Sun and to the galaxy, with special emphasis on galactic cosmic rays and the anomalous nuclear component in the solar system. We have determined the age of the galactic cosmic rays. The galactic cosmic ray nuclei are the only sample of matter from the galaxy that can be investigated directly from within the solar system. The elemental and isotopic composition of galactic cosmic rays are investigated with spacecraft experiments (currently, Pioneer 10, IMP 8, and Ulysses over the poles of the Sun) (1) to determine the isotopic cosmic ray matter, (2) to test models of nucleosynthesis in stars, (e.g., explosive nucleosynthesis), and (3) to investigate composition of matter in the solar atmosphere by means of solar flares and coronal mass ejections. Experimental investigations on the electrodynamics of interplanetary space and the control of cosmic ray fluxes by the Sun are carried out on the deep space probe Pioneer 10 (extending to 68 astronomical units) and the Ulysses spacecraft to study heliospheric dynamics and cosmic ray modulation in three dimensions. With our instruments on man's first mission over the poles of the solar system, the International Solar Polar Mission, we have explored the heliospheric regions over the south and north solar poles and discovered new aspects of galactic cosmic ray propagation through the heliosphere. Our invention of a new concept for detection and mass measurement of cosmic dust has led to our instruments being included on two U.S.S.R. space probes that encountered the coma of Halley's Comet in March 1986. These cosmic dust instruments are carried on the Cassini Spacecraft (launched in 1997) to study the origin of the rings of Saturn in 2004-08. The Ulysses investigations will continue through year 2002, with a second pole-to-pole pass over the Sun when it is active. Undergraduate and graduate students participate in these researches. Our dust experiments are on the stardust mission to Comet Wild-2 in 2004. Simon P. SwordyMy research is directed to observations and analysis of cosmic rays mainly through the following experimental efforts. I am involved with several projects to make direct measurements of cosmic ray particles using spacecraft and balloons: The HEAT experiment is an effort, together with Professor Müller, which is aimed at the detection of antiparticles in cosmic rays with a superconducting magnet on a high altitude balloon. We have successfully measured the fraction of positrons at high energy and have several recent publications on the results of this work. Unlike previous observations our measurements indicate that the bulk of positrons at high energy are secondaries of proton interactions within our Galaxy. There is however still a small unexplained excess near 10 GeV which could be from some primary source. This speculation is the subject of a recent paper. A new version of HEAT which has been redesigned and optimized for the detection of antiprotons is expected to be flown in Spring 1999 on a high-altitude balloon. This uses state-of-the-art electronics to provide several thousand channels of low-power signal acquisition during the flight. The TRACER experiment is a payload for a long-duration (14-day) high-altitude balloon flight around the North Pole with a launch site in Alaska. This experiment uses the technique of transition radiation to detect the energy spectra of heavy nuclei in cosmic rays of energies above 1 TeV. These measurements are expected to reveal key issue on the origin of cosmic rays when the flight is complete in Fall 1999. One novel aspect of this payload is the use of thin-walled gas proportional tubes which can operate in a vacuum for the transition radiation detector. This allows the payload to fly without a heavy-pressure vessel. The RICH experiment has flown three times in recent years on a single-day high-altitude balloon flight. This was the first Ring Imaging Cherenkov detector flown outside the atmosphere. The purpose of these flights was to obtain accurate measurements of the energy spectra of light cosmic rays. The results are in preparation for publication at present. The CREAM experiment is a new experiment which combines transition radiation and thin calorimetry to measure cosmic rays near the "knee" of the spectrum at 1000 TeV. This is planned for future 100-day ultra-long-duration balloon flights. This experiment is presently under development in collaboration with Penn. State and the University of Maryland. ACCESS is a cosmic ray experiment planned for the International Space Station. This will be the largest experiment on the Space Station at about 11,000 lbs. launch weight. The science goals include the measurement of all cosmic ray nuclei into the "knee" of the overall spectrum. At present this instrument is under study at NASA for launch in 2007. I am also involved with indirect measurements of cosmic ray nuclei through the following: The DICE experiment operated for nearly three years (1994-97) at the Dugway, Utah site of the Chicago Air Shower Array (CASA). This experiment was specifically designed to detect changes in cosmic ray composition across the knee of the spectrum. The results indicate that contrary to expectation the mean mass of cosmic rays tends to decrease slightly across this spectral feature. Recent efforts at correlations of the DICE measurements of atmospheric Cherenkov with particles at ground level have supported these composition measurements. Future developments of Cherenkov imaging of air showers are being explored. The VERITAS experiment is a collaboration formed to build the next generation of atmospheric Cherenkov telescopes for gamma ray measurements. This will consist of an array of telescopes located near Tucson in Arizona which can be used for gamma ray detection on dark, moonless nights. VERITAS can be used to directly search the putative supernova remnant sources of cosmic rays for the gamma rays expected to be produced at these sites. The level of sensitivity of VERITAS is sufficient to determine whether or not hadrons are accelerated to energies near 1000 TeV in these sources as expected in the "standard model" of Galactic cosmic rays. Michael S. TurnerSee Department of Astronomy and Astrophysics Yau W. WahMy research centers around neutral kaon rare decays with emphasis on the question of charge-conjugate-Parity (CP) violation. The decay modes of kaon into a neutral pion and a pair of leptons are particularly interesting in that they are CP violating, but have never been seen. A series of experiments have been conducted at the nearby Fermi National Accelerator Laboratory. The current experiment has the best sensitivities for a large variety of kaon and pion decay modes and provides unprecedented high sensitivity studies of particle properties and searches for violations of basic symmetries. Robert M. WaldMy research mainly has focused upon the theory of quantum phenomena in strong gravitational fields, particularly quantum effects involving black holes and black hole thermodynamics. My interests also span attempts to formulate a quantum theory of gravitation (where no background classical metrical or causal structure of spacetime is present), mathematical investigations of classical general relativity, and applications of general relativity to cosmology and astrophysics (such as gravitational lensing phenomena and gravitational radiation reaction effects). Paul WiegmannMy research focuses on the non-perturbative aspects of quantum field theory, primarily electronic systems with strong interaction. This includes physics in low dimensions, quantum magnetism, quantum Hall effect, and strongly correlated electronic systems-in condensed matter as well as completely integrable models of quantum field theory and statistical mechanics, quantum groups, anomalies in quantum field theory, topological field theories, and solitons' nonlinear dynamics-in mathematical physics. Since 1987 I have been involved in the theory of high temperature superconductivity based on the theory of strongly correlated electronic systems. Bruce WinsteinWe have been engaged for the past several years in precise studies of very small symmetry violations. CP symmetry, which reverses left and right and changes particles into antiparticles, was shown to be violated in 1964 by James Cronin and colleagues. The only known manifestation of this violation is in the transition from the neutral kaon to its own antiparticle: that transition amplitude differs from the "time reversed" one by 0.23%. CP violation is important in that it likely accounts for the lack of antimatter in the universe: there is a force which distinguishes matter from antimatter. Along with Professors Blucher, Wah, and Winston and investigators at ten other institutions, we constructed a new detector (KTeV) which was designed to detect another manifestation of CP violation if our understanding of the mechanism (Standard Model) is correct. The core of the new experiment is an array of 3100 CsI crystals to precisely measure the energies of high energy gammas from kaon decays. The work on the crystals and on the electronics for triggering purposes was carried out on the campus. The Fermilab experiment, which also studies a host of very rare kaon decays, ran in 1997 and will be upgraded for runs in 1999 and beyond. Recently we reported on the analysis of 20% of the data collected to isolate this new form of CP violation, called direct CP violation. In a seminar given by my student Peter Shawhan at Fermilab on February 24, 1999, we announced a definitive measurement of the quantity epsilon prime divided by epsilon. The result-0.00280 with an error of ±0.00041-serves to establish direct CP violation at nearly seven standard deviations. Roland WinstonSolar energy. The new discipline of nonimaging optics makes it possible to concentrate sunlight in excess of solar surface intensities. Our group is using ultra high solar flux to pump lasers and generate very high temperatures. Nontracking collectors are being developed for solar cooling. Experimental particle physics. The weak interactions of hyperons provide an important testing ground for theories of the symmetry and structure of elementary particles. Our group is participating in precision studies of neutral kaon and hyperon decays. Thomas A. WittenMy research concerns the statistics of "structured" fluids, containing polyatomic species such as polymers, surfactant micelles, or colloidal particles and aggregates. One current interest is heterogeneous polymers, in which competing interactions give novel structures and metastability to a polymer fluid. We are studying new structures that such polymers take on when they are near a solid substrate. We are studying the consequences of topological and packing constraints in polymer fluids: orientational coupling, entanglement, and twisting. We are also studying the mechanics of crumpled elastic membranes and of rubber filled with rigid colloidal aggregates. We wish to understand the distinctive ways in which stress propagates and relaxes in these materials to give them their distinctive strength characteristics.
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