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Graduate Student Research
Research opportunities for graduate students abound. In addition to working directly with a Physics Department faculty member, graduate students also have access to research taking place in Astronomy & Astrophysics, Chemistry, Mathematics, Geophysical Sciences, Biological Sciences, Medical Physics, Computer Science, as well as at Fermilab, Argonne, CERN, and many other departments, facilities, observatories, and laboratories.
In many cases, graduate students can get involved in research immediately upon, and sometime before, beginning his or her first quarter in our program; this is especially true for students interested in experimental research. Theory students, depending on the area, may need to take a few courses before settling down into a research project.
The best way for graduate students to get involved in the research of his or her choice is to talk to the faculty members working in their area(s) of interest and find out how to best proceed based on his or her background and specific situation. A great way to explore an experimental research group early-on is to satisfy the experimental physics requirement by doing a year-long research project with that group.
Below, you will find a sampling of some of the fore-front-level research being done by our graduate students. You may also view the graduate research archive for previous profiles. Enjoy…
- Mathew Becker
- Shanthanu Bhardwaj
(condensed matter theory)
- Callum Quigley
- B.S., University of Michigan, 2007 (Physics)
- B.S., University of Michigan, 2007 (Mathematics)
- M.S., University of Chicago, 2008 (Physics)
Graduate Student (2007-pres), Dept. of Physics, Kavli Institute for Cosmological Physics
Research: Astrophysics & Cosmology
Awards: GAANN Fellow (Dept. of Ed), Illinois Space Grant Consortium Graduate Fellow, Sugarman Award (EFI)
Research Advisor: Andrey Kravtsov
Since the discovery of dark energy and the acceleration of the Universe in 1998 by two teams studying high-redshift Type Ia supernovae, Cosmic Microwave Background experiments and low-redhsift observations of structure formation from large area sky surveys have converged on a standard cosmological model, LambdaCDM. While this model provides convincing explanations for the formation of galaxies and large scale structure, the matter from which we are made along with a small amount of known relativistic particles compose only ~5% of the total mass-energy density of the Universe. The rest comprises two of the great mysteries in cosmology - dark matter and dark energy - each being ~25% and ~70% respectively of the total mass-energy density of the Universe.
Cosmology is now entering the era of large area sky surveys which will cover a quarter of the sky or more at unprecedented sensitivity, observing in multiple wavelengths of light. These surveys, like the South Pole Telescope, the Dark Energy Survey, and the Large Synoptic Survey Telescope, will give us a new view of the Universe at the age when dark energy came to be the dominant fraction of the total mass-energy density and thus will provide strong constraints on the nature of dark energy. Two of the most promising techniques to study dark energy and the growth of large scale structure in the Universe with these surveys rely on an effect called weak gravitational lensing (the tiny deflections of photons from background galaxies by large clumps of matter along the line-of-sight between us and distant galaxies). The first technique is called cosmic shear and involves directly measuring and cross-correlating these weak lensing signals. The second technique involves counting the number of galaxy clusters, the largest gravitationally bound objects in the Universe, as function of their mass. Weak lensing measurements are one of the best ways to determine the masses of galaxy clusters and are thus crucial to using counts of galaxy clusters to constrain the properties of dark energy.
Unfortunately, the upcoming measurements of cosmic shear and the counts of galaxy clusters are expected to be dominated by systematic as opposed to random, statistical errors. Understanding these errors requires, in part, the use of large supercomputer N-body simulations which model the formation of largest scale structures in the Universe and the effects of dark energy on this process. I use these simulations to study both cosmic shear and as well as weak lensing techniques that determine the total mass contained in galaxy clusters. As a graduate student in the Kavli Institute for Cosmological Physics, I have developed and implemented new, specialized methods for calculating the expected weak lensing signals from these N-body simulations for large area sky surveys. These weak lensing calculations, which on single computer would take years to complete, for the first time now finish in a few days to a week enabling the production of ensembles of N-body simulations with weak lensing.
With the Dark Energy Survey, I have been working to build a large ensemble of N-body simulations of different phenomenological dark energy models with these self-consistently calculated weak lensing signals. These weak lensing calculations are being used by the Dark Energy Survey Collaboration to study systematic effects in both cosmic shear signals and also weak lensing galaxy cluster mass estimates in order to test and understand how accurately the properties of dark energy can be constrained. In addition to their use by the Dark Energy Survey, they have also been used by the South Pole Telescope Collaboration for studies of a different, but related effect called Cosmic Microwave Background lensing.
In addition to the numerical work described above, I have worked on a new family of methods for analyzing cosmic shear data from these large area sky surveys. This new family of methods for cosmic shear accounts for observational effects in cosmic shear measurements, like the binning of the data. It also allows for the clean separation of systematic signals, called B-modes, from the signals due to General Relativity, called E-modes, in the presence of complicated survey window functions and biased sampling of the cosmic shear field. Additionally, this new family of methods is significantly simpler to use and implement than previous methods, which should make them broadly applicable to upcoming cosmic shear surveys.
Finally, I also work on continuing analyses of the data from the Sloan Digital Sky Survey. These analyses provide consistency tests of the current cosmological model and key constraints on the amplitude of matter fluctuations in the low redshift Universe. These constraints, along with the experience and understanding gained by working with low redshift data, will allow us to make the most of the data from upcoming large area sky surveys. The next decade will be an exciting time for cosmology with an enormous amount of data from new surveys and potentially new discoveries about the nature of dark energy.
- Cosmic Shear E/B-mode Estimation with Binned Correlation Function Data. M. R. Becker 2012, MNRAS, submitted [arXiv:1208.0068]
- Cosmological Constraints from the Large Scale Weak Lensing of SDSS MaxBCG Clusters. Y. Zu, D. H. Weinberg, E. Rozo, E. S. Sheldon, J. L. Tinker, M. R. Becker 2012, MNRAS, submitted [arXiv:1207.3794]
- A High Throughput Workflow Environment for Cosmological Simulations. B. M. S. Erickson, R. Singh, A. E. Evrard, M. R. Becker, M. T. Busha, A. V. Kravtsov, S. Marru, M. Pierce, R. H. Wechsler 2012, in Proceedings of the 1st Conference of the Extreme Science and Engineering Discovery Environment: Bridging from the eXtreme to the campus and beyond, XSEDE 12 (New York, NY, USA: ACM), 34:1-34:8
- A Measurement of the Correlation of Galaxy Surveys with CMB Lensing Convergence Maps from the South Pole Telescope. L. E. Bleem, A. van Engelen, G. P. Holder, K. A. Aird, R. Armstrong, M. L. N. Ashby, M. R. Becker, et al. 2012, ApJ, 753, L9 [arXiv:1203.4808]
- Cosmological Constraints from Galaxy Clustering and the Mass-to-Number Ratio of Galaxy Clusters. J. L. Tinker, E. S. Sheldon, R. H. Wechsler, M. R. Becker, E. Rozo, Y. Zu, D. H. Weinberg, I. Zehavi, M. Blanton, M. Busha, B. P. Koester 2012, ApJ, 745, 16 [arXiv:1104.1635]
- On the Accuracy of Weak Lensing Cluster Mass Reconstructions. M. R. Becker & A. V. Kravtsov 2011, ApJ, 740, 25 [arXiv:1011.1681]
Degrees: M.Sc., Indian Institute of Technology-Kanpur, 2007 (Physics)
Graduate Student (2007-pres), Dept. of Physics, James Franck Inst.
Research: Condensed Matter Theory
Awards: Michelson Fellow, Wentzel Research Prize (Dept. of Physics)
Research Advisor: Ilya Gruzberg
My research interests lie broadly in theoretical condensed matter physics. The idea that systems composed of well understood constituents can still behave in ways which are difficult to predict was perhaps most famously expressed in Phil Anderson's "More is Different" mantra. The variety of electrical behaviour from metals, insulators, and semi-conductors to more interesting phases like superconductors, and topological insulators in systems made up of electrons and nucleons with all their physics governed by electromagnetism, proves that more is indeed different.
One of the most interesting systems is the critical state of the Integer Quantum Hall Effect. Although the initial prediction of the quantization of transverse conductivity in the presence of a magnetic field is nearly forty years old, the exact nature of the quantum hall state and the associated critical exponents is still unknown. My research has largely been in trying to work on understanding this and hopefully connecting it to a conformal field theory that can predict the nature of these critical exponents. There are several different approaches to this problem, and the one I have been working on is to attempt to describe the behaviour of these systems by using 'network models'. These simple discrete models - based on Chalker and Coddington's network model to describe the Quantum Hall transition at strong magnetic field - capture the essential physics of the system. We then attempt to construct such a discrete model that captures all the relevant behaviour of the system we wish to understand and use this to guide us to the appropriate conformal field theory (CFT) describing the transition at the critical point.
Several of the mathematical techniques involved in studying the Quantum Hall Effect are also applicable to other systems of interest in 2-dimensions, and that is one of the future avenues of interest for me.
- B.Sc., University of Toronto, 2003 (Physics)
- B.Sc., University of Toronto, 2003 (Mathematics)
- M.Sc., University of British Columbia, 2005 (Physics)
- M.Sc., University of Toronto, 2006 (Mathematics)
Graduate Student (2006-pres), Dept. of Physics, Enrico Fermi Institute
Research: String Theory
Awards: Robert R. McCormick Fellow, Robert G. Sachs Fellow, NSERC Postgraduate Scholar, Gregor Wentzel Research Prize, Sidney Bloomenthal Fellow
Research Advisor: Savdeep Sethi
My research at the University of Chicago has focused on string theory, which is a branch of physics that begins with the simple question, “What if, instead of point-like particles, everything was made of tiny, one-dimensional, vibrating strings?” By demanding self-consistency of the theory, this one simple assumption leads to a spectacular framework that unifies all the ingredients one might expect in a fundamental theory of Nature, including non-Abelian gauge theories coupled to chiral fermions (as we have in the Standard Model), and most amazingly a quantum-mechanical theory of gravity.
One curious requirement that the consistency of the theory imposes is that there must exist six spatial dimensions beyond the three that we observe. Including time, this means string theory must live in a ten-dimensional spacetime. So what happens to all those extra dimensions? The most common answer goes back nearly a hundred years (well before the advent of string theory) to Kaluza and Klein, who suggested that extra dimensions may be curled up into a compact manifold so small we cannot detect them. To understand this idea better, it helps to think of a garden hose: we know that the surface of the hose has two dimensions, but from very far away you will not be able to resolve its circumference and you might think it only has extent in one direction. In this simple analogy, the “extra” dimension of the hose has been compactified into a small circle. In string theory the same idea applies, but the geometry of the six-dimensional space is usually much more non-trivial. All of this would seem an unnecessary complication if not for the fact that the geometry of the compactified space actually determines the number, masses and interactions of the particles we observe in our four-dimensional (non-compact) spacetime.
Unfortunately the simplest, and best studied, solutions with compactified extra dimensions have a fatal flaw: for each inequivalent way one can deform the geometry of the internal space there is a corresponding massless scalar particle, in the four-dimensional spectrum. These scalar fields are called moduli. This is a phenomenological disaster, as we have observed precisely zero massless scalar particles in Nature. Fortunately, string theory offers a remedy, which is the following. In addition to gravity, string theory contains generalizations of electromagnetic fields, as well. Turning on non-trivial fluxes of these generalized magnetic fields can lead to solutions where parts of the geometry can no longer be deformed. Thus the troublesome moduli fields are eliminated. These flux compactifications currently offer the best hope of connecting string theory solutions with real world particle physics and cosmology.
One powerful approach to studying the dynamics of a string is to consider the quantum field theory (QFT) that lives on its two-dimensional worldsheet, which is analogous to a point-particle’s one-dimensional worldline. This works extremely well in simple situations like flat spacetime, but for more involved backgrounds, such as flux compactifications, this is essentially impossible to carry-out directly. A large part of my research with Prof. Sethi and collaborators focuses on developing tools to study the worldsheet theories of flux compactifications that bypass these difficulties. The basic idea is to find a simpler two-dimensional QFT that reduces to the one you are interested in a certain limit. Then it is possible to carry out computations in the simple description, and then take the appropriate limit to extract information about the flux compactification. With this tool we have been able to build new classes of flux backgrounds, and have begun to study their properties. One feature we have discovered so far is that these models do indeed have less moduli than their counterparts without flux, which is a reassuring confirmation of we expected. Much still remains to be discovered in these models, and they are still under intense investigation.
Rather than pulling everything back to the worldsheet, it is also possible to study string theory directly in its ten-dimensional spacetime. In principle this would require a string field theory, which would capture the infinite tower of vibrational modes of the string at each point in spacetime. However at low energies it suffices to consider only the lowest excitations of the string, which are all massless states. Some of these include the graviton (the force carrier for gravity, analogous to the photon for E&M), the generalized electromagnetic fields used in flux compactifications, and the moduli fields (if present). The effective description of these massless states is captured by a ten-dimensional QFT called supergravity, which is a supersymmetric extension of Einstein’s theory of General Relativity. String theory corrects the supergravity action by an infinite set of higher-derivative terms, which are all suppressed by the Planck scale. This expansion is valid so long as we restrict to low energy phenomena, and the curvatures of spacetime remain small.
Another aspect of my research uses this expansion to investigate how supergravity results are modified once the leading higher-derivative corrections are taken into account. Our most recent result on this topic, together with Prof. Martinec and another graduate student, is an application of this idea to cosmology. It has been known for decades that supergravity alone cannot lead to accelerated expansion of the Universe, contrary to what we observe. We asked if higher-derivative interactions might improve the situation. We found that if we ignore the dynamics of everything but the four-dimensional metric, effectively freezing all the other supergravity fields at some fixed values, then accelerated expansion is not possible. This rules out the possibility of finding de Sitter solutions in a wide class of string backgrounds where the supergravity approximation is valid. This strongly indicates that in order to build de Sitter vacua, and make contact with the real world, we cannot truncate string theory to just the massless sector. Instead we need a complete description of the theory, such as the two-dimensional approach discussed above.
- C. Quigley, S. Sethi, M. Stern, “Novel Branches of (0,2) Theories,” JHEP 1209 (2012) 064, [arXiv:1206.3228].
- S. R. Green, E. J. Martinec, C. Quigley, S. Sethi, “Constraints on String Cosmology,” Class. Quant. Grav. 29 (2012) 075006, [arXiv: 1110.0545].
- C. Quigley, S. Sethi, “Linear Sigma Models with Torsion,” JHEP 1111 (2011) 034, [arXiv: 1107.0714].
- L. Anguelova, C. Quigley, “Quantum Corrections to Heterotic Moduli Potentials,” JHEP 1102 (2011) 113, [arXiv: 1007.5047].
- L. Anguelova, C. Quigley, S. Sethi, “The Leading Quantum Corrections to Stringy Kahler Potentials,” JHEP 1010 (2010) 065, [arXiv: 1007.4793].
- B.A., University of Chicago, 2007 (Physics with Honors)
- B.S., University of Chicago 2007 (Mathematics)
Graduate Student (2007-pres) Dept. of Physics, Enrico Fermi Institute
Research: Accelerator Physics
Awards: Robert R. McCormick Fellow, Robert G. Sachs Fellow, Gaurang & Kanwal Yodh Prize (Dept. of Physics)
Research Advisors: Young-Kee Kim and Wim Leemans
State of the art particle accelerators are used in many scientific disciplines including biology, materials science and particle physics. Improved understanding of plasma physics and advances in laser technology opened up a new field of R&D for the next generation of accelerators. Under the faculty advisory of Professor Young-Kee Kim and research supervision of Dr. Wim Leemans, I study laser-plasma accelerators (LPAs) at the LOASIS Program at Lawrence Berkeley National Laboratory.
Experimental investigation of LPAs is a topic pushing the limits of physics and technology. In 1979, Tajima and Dawson proposed an idea to use the 4th state of matter, plasma, as a medium to exchange electromagnetic energy into the kinetic energy of charged particles. In principle, this novel concept offered a potential to reduce the size of accelerators by a factor of a thousand: plasma can sustain thousands times larger electric fields than a conventional radio-frequency cavity. Experimental investigation of LPAs advanced rapidly since the 1990’s following the invention of the chirped-pulse amplification (CPA) technique to produce ultra-high intensity laser pulses. Employing a hydrogen-filled capillary waveguide, high-quality electron beams (e-beams) of energy in the GeV’s have been produced within a few centimeters. Today, improved understanding of plasma physics and rapidly advancing laser technologies are producing higher and higher intensity laser pulses and continue to expand the realm of LPA experiments
Currently, I participate in experiments using 100 TW-class, 40 fs laser pulses to understand and diagnose laser propagation in plasma with application to future high-energy accelerators. My thesis topic, referred to as staging of LPAs involves adding a second, independently driven laser acceleration stage to boost the electron energy from the primary stage. So far, LPA experiments have been done using only a single driving laser pulse. Staging is necessary because, by exciting plasma wakes, a driving laser pulse transfers energy in plasma such that it eventually becomes too weak to excite wakefields. The staging experiment involves precise control of two high intensity short laser pulses and plasma modules, coupled in a very compact manner using a disposable plasma mirror. This experiment represents a milestone in the development of LPAs and makes LPAs even stronger candidates for the next generation accelerator technology.
An understanding of laser-plasma interaction using the laser profile and its spectra is another of my research topics. Plasma is a dynamic accelerating structure that changes with time as well as with the shape and the strength of the driving laser pulse. This dynamic nature of the plasma structure represents a freedom and also a challenge in controlling the particle acceleration, and a single-shot diagnostic of the plasma wave is critical. By comparing how the driving laser pulse changes in shape and color before and after the interaction with plasma, we intend to deduce the properties of the excited wakefield structure. In particular, we learn about the energy transfer from laser to plasma and obtain a measure of electric field amplitude. Along with simulation studies, the shape of accelerating structures can be inferred. Understanding the laser-plasma interaction and the development of a single-shot diagnostic using laser spectra are complex topics but critical for the successful development of LPAs.
- A. J. Gonsalves, K. Nakamura, C. Lin, D. Panasenko, S. Shiraishi, T. Sokollik, C. Benedetti, C. B. Schroeder, C. G. R. Geddes, J. van Tilborg, J. Osterhoff, E. Esarey, C. Toth, W. P. Leemans, "Tunable Laser Plasma Accelerator based on Longitudinal Density Tailoring," Nature Physics (2011).
- A. J. Gonsalves, K. Nakamura, C. Lin, J. Osterhoff, S. Shiraishi, C. B. Schroeder, C. G. R. Geddes, Cs. Toth, E. Esarey, W. P. Leemans, "Plasma Channel Diagnostic Based on Laser Centroid Oscillations," Phys. Plasmas 17, 056706 (2010).
- G. R. Plateau, N. H. Matlis, C. G. R. Geddes, A. J. Gonsalves, S. Shiraishi, C. Lin, R. A. van Mourik, and W. P. Leemans, "Wavefront-sensor-based electron density measurements for laser-plasma accelerators," Rev. Sci. Instrum. 81 (3), 033108 (2010).
Degrees: B.S., University of Arizona 2007 (Physics)
Graduate Student (2007-pres), Dept. of Physics, James Franck Inst.
Research: Experimental Soft-Condensed Matter Physics
Awards (U-Arizona): Outstanding Senior, Outstanding Research Presentation, Honors Transfer Scholarship
Awards (grad): Bruce Winstein Prize for Instrumentation, Robert A. Millikan Fellow, Robert R. McCormick Fellow, Robert G. Sachs Fellow (Dept. of Physics), Best Speaker (Electrostatics Society of America)
Research Advisor: Heinrich Jaeger
I work in experimental soft-condensed matter physics. As its name suggests, soft-condensed matter physics deals materials that are in some sense "softer" than those studied in hard-condensed matter. Whereas the latter is primarily interested in crystalline solids, we study things like glasses, fluids, foams, gels and granular matter. In a more abstract way, our field is soft in the sense that there is no one solid foundation on which its study is based.
My graduate research in soft-matter has parallels to this description. Rather than being tied to a single thesis topic, I have been able to chase a number of my creative interests, ultimately tying together three major projects. While these three projects are all quite different on the surface, they all are united by the common theme of shedding light on the physics of phenomena to which everyone has some familiarity yet little understanding.
The first project I worked on sought to explain a puzzling observation: grains of sand, when flowing out as a stream from a small hole, will undergo an instability to form droplets, just like water slowly flowing from a faucet and tip-tapping on the bottom of the kitchen sink. This phenomenon is totally unexpected given that macroscopic grains, unlike fluids, have typically been thought to lack surface tension. With the aid of a "freely-falling laboratory", atomic force microscope measurements detailing the nanoscale forces between these grains, and large-scale molecular dynamics simulations, my labmates and I were able to show that streams of grains do in fact have a microscopic surface tension. Although it is orders of magnitudes smaller than that of common fluids, it works in conjunction with gravitational stretching to cause the stream to break up.
In my next project, I became interested in a dark little secret that physicists have known about for a long time. We all know that rubbing two different materials together will lead to tribocharging, i.e. the exchange of electrical charge. Surprisingly, if you rub two identical materials together, more often than not they also exchange charge and often in a systematic way. I studied this phenomenon in the context of a large ensemble of grains, a system where charging can lead to intense displays of lightning in volcanic clouds, huge electric fields in dust storms and cyclones, and terrible disasters such as silo explosions. By building a high-tech, ultra sensitive version of the Millikan Oil Drop experiment for macroscopic grains, I was able to measure the charge of and size of such grains simultaneously. Our work shows conclusively that the charging of grains is related to the grain size; in a binary-sized systems, large grains charge positively and small negatively. As a last step toward understanding this curious phenomenon, we are working on proving or disproving a longstanding model involving the non-equilibrium transfer of trapped-state electrons.
My final project found its inspiration on YouTube, where a short search reveals that a pool of cornstarch grains mixed with water creates an amazing substance. This material is fluid-like when perturbed lightly, but hardens when driven strongly, allowing people to run across as if they were walking on water. Although this type of shear-thickening fluid has been studied extensively in a purely rheological context, I wanted to know exactly how someone can run across its surface. I built a simple experiment to test this. By shooting a rod into a large vat of this oobleck and using an arsenal of high-tech equipment to study the impact, I was able to show that this phenomena is driven by the dynamic solidification of the cornstarch suspension. This impact-activated solidification is totally counterintuitive. Whereas most granular materials are fluidized by a sudden input of energy, this granular suspension is instead solidified. The momentum of the impacting object is quickly taken away as it causes this solid to grow and move, making these types of materials ideal for stress-response applications.
- Waitukaitis, S.R. et al. Direct measurement of size-dependent, same-material tribocharging in insulating grains, in preparation.
- Waitukaitis, S.R., Castillo, G.M., & Jaeger, H.M. A Granular Electrometer: Measuring the Charge Distribution of a Pile of Grains, in preparation.
- Waitukaitis,S.R. & Jaeger,H.M., Solidificación de una suspensión de maicena y agua, Revista Cubana de Física, (2012).
- Waitukaitis, S.R., & Jaeger, H.M. Impact-activated solidification in dense suspensions via dynamic Jamming Fronts, Nature 487, 205-209 (2012).
- Waitukaitis, S.R. et al. Droplet and cluster formation in freely falling granular streams, Phys. Rev. E 83, 051302 (2011).
- Royer, J.R.R. et al. High-speed tracking of rupture and clustering in freely falling granular streams, Nature 459, 1110-1113 (2009).
- des Jardins, A.C. et al. Reconnection in three dimensions: The role of spines in three eruptive flares, Astrophys. J. 693, 1628-1636 (2009).
- Carr, A et al. Cover slip external cavity diode laser, Rev. Sci. Instrum. 78, 106108 (2007).
- B.S., Ohio State University 2008 (Physics)
- B.S., Ohio State University 2008 (Astronomy)
- M.S., University of Chicago 2009 (Physics)
Graduate Student (2008-pres), Dept. of Physics, Enrico Fermi Inst.
Research: Astroparticle Physics
Awards: Michelson Fellow, Robert G. Sachs Fellow, Eugene & Niesje Parker Fellow, Gaurang & Kanwal Yodh Prize (Dept. of Physics), Price Prize (Ohio State)
Research Advisor: Paolo Privitera
At the highest energies, sources of cosmic rays should be among the most powerful accelerators in the universe, but even after a century of observation their origin and composition remains a mystery. Large observatories have revealed a flux suppression above a few 10^19 eV, similar to the expected effect of the interaction of ultrahigh energy cosmic rays (UHECRs) with the cosmic microwave background. To answer the question of the origin of UHECRs, the flux suppression must be overcome with even larger instrumented areas to obtain a large sample of high quality data.
Our work at the University of Chicago as a member of the largest of these cosmic ray observatories, the Pierre Auger Observatory, has helped to measure the largest sample of cosmic ray induced extensive air showers at the highest energies. Auger instruments an area of 3000 square kilometers in Mendoza Province, Argentina with an array of surface detectors and fluorescence telescopes. This data has been used to make a precise measurement of the energy spectrum, find hints of spatial anisotropy, and a discover surprising change in the chemical composition at the highest energies.
My research at the University of Chicago has focused on new techniques for detecting extensive air showers that will lead to a larger sample of high quality UHECR data. We are developing new radio detectors which promise 100% duty cycle and measurement quality similar to the fluorescence detection technique. This would allow for collection of much greater amounts of data that could be used to understand the origin and composition of cosmic rays. By combining electronics from high energy physics with commercially sourced radio components, we have built and tested the MIcrowave Detection of Air Showers (MIDAS) experiment, a prototype wide field of view imaging camera deployed on the roof of the Kersten Physics Teaching Center on campus. The imaging camera operates in the commercial C-Band (3.4 to 4.2 GHz) covering a 20 degree by 10 degree field of view. This is instrumented with RF power detectors and 20 MHz flash analog-to-digital converters. The digitized signal is passed through a field programmable gate array which is used to form a trigger looking for topological patterns which match the microsecond tracks crossing the field of view expected from extensive air showers. With 61 days of live time data from this set-up we were able to set new limits on isotropic microwave emission from extensive air showers, ruling out the putative power flux and coherence values at greater than five sigma. The MIDAS detector has now been deployed at the Pierre Auger Observatory where it will run in coincidence with both the surface detector and fluorescence detector, continuing to search for microwave emission from extensive air showers.
Our group has also focused on test beam measurements at Argonne National Laboratory (ANL) seeking to detect isotropic microwave emission from a particles in the laboratory setting which simulate an extensive air shower. The Microwave Air Yield Beam Experiment (MAYBE) passed 3 MeV electrons from the Van de Graaff accelerator of the Chemistry Division of ANL through an RF anechoic chamber to measure the microwave emission. With these tests we were able to measure the flat spectral nature of the emission from 1 to 15 GHz and observe that the emission is unpolarized. This is information that was speculated but not previously measured. The emission was also observed to scale linearly with energy deposit. The results of this experiment will be used to guide the design of microwave detectors for UHECRs.
- J. Alvarez-Muñiz et al. “Search for microwave emission from ultrahigh energy cosmic rays”. Phys. Rev. D 86, 051104 (2012), arXiv:1205.5785.
- J. Alvarez-Muñiz et al. “The MIDAS telescope for microwave detection of ultra-high energy cosmic rays”. Submitted to Astroparticle Physics (2012), arXiv:1208.2734.