Colloquia / Seminars
Tea, coffee, and refreshments are served at the speaker’s reception in Phillips Hall 269, 3:30pm.
Colloquia are held Monday afternoons in Phillips Hall 265, 4:00pm.
The student Questions and Answers will also be held in Phillips Hall 269 after the colloquium, 5:15pm.
Past Spring 2019 Colloquia
Going with the flow: making the path integral more complex
Gökce Basar, University of Illinois, Chicago
The theory of strong interactions (Quantum Chromo Dynamics, or QCD), which describes how the constituents of protons and neutrons (quarks and gluons) interact, has been around for more than 40 years. However, the calculation of the properties of nuclear matter in various phases from QCD remains an unsolved problem. These phases include quark gluon plasma, the phase that filled the universe microseconds after it was formed, and dense nuclear matter, which exists in the cores of compact stars. The reason these calculations remain elusive is an infamous obstacle called the ‘sign problem.’ In this talk, I explore a new way of tackling the sign problem that involves generalizing the Feynman path integral to complex fields. I discuss both conceptual and computational aspects of this new approach, and give examples of interacting quantum field theories where it successfully solves the sign problem, with the goal of eventually using it to solve QCD.
Weighing a Ghost: The Quest to Measure the Neutrino Mass
Walter Pettus, University of Washington
The ghostly neutrinos remain the only fundamental fermions whose masses are unknown. Neutrino oscillation measurements definitively demonstrate neutrinos have mass, breaching the Standard Model of Particle Physics, but cannot determine that mass scale. The most sensitive searches to date have placed limits on the neutrino mass, indicating they are at least six orders of magnitude lighter than the next fermion. If neutrinos possess the unique property of being their own antiparticles, this vast scale difference is a clue to the new physics of their mass generation mechanism.
I will review the status of experiments to measure the neutrino mass scale, with particular emphasis on laboratory probes. Project 8 is an experimental program developing next-generation sensitivity to the neutrino mass through measurement of the kinematic beta endpoint, a model-independent probe of the mass scale. Complementary to this technique are searches for neutrinoless double beta decay, where I will detail the 76Ge program, advancing from the currently operating Majorana Demonstrator to the LEGEND experiment in preparation.
Searching for dark matter with liquid argon
Graham Giovanetti, Princeton University
The DarkSide collaboration has undertaken a staged program using argon time projection chambers (TPCs) to search for dark matter. I will introduce DarkSide-50, a 50 kg dual-phase argon TPC that has been operating since mid-2015 at LNGS, and present recent results from this detector. Then I will discuss the implications of these results for a next-generation experiment, DarkSide-20k, a more than 20 tonne fiducial mass TPC equipped with SiPM-based photosensors.
Low Temperature Searches for Physics Beyond the Standard Model
Danielle Speller, Yale University
The standard model of particle physics provides a useful framework for understanding the known particles and their interactions, and heavily informs our understanding of early universe cosmology. Nevertheless, key questions remain unanswered, including the nature of dark matter and the origin of the matter-antimatter asymmetry.
New developments in quantum measurement technologies and the maturation of low-noise cryogenic techniques allow us to directly and sensitively explore low-energy astrophysical and laboratory interactions, addressing these questions and others with enhanced searches for new particles and rare decays. In particular, dark matter and rare-event searches benefit from these advancements in technology.
The CUORE (Cryogenic Underground Observatory for Rare Events) Experiment is a ton-scale, 988-bolometer array located deep underground in Gran Sasso National Laboratory (LNGS). CUORE is designed to search for the neutrinoless double-beta decay (0νββ) of 130-Te, a lepton number violating process that could shed light on the asymmetry between matter and antimatter and point toward new physics. Another search, the Haloscope At Yale Sensitive To Axion CDM (HAYSTAC) is a microwave cavity experiment sensitive to significant regions of the cosmologically favored mass range for an axion dark matter candidate. HAYSTAC also serves as a pathfinder experiment for the application of new technologies to axion searches, and is now entering its second phase of operation. I will discuss the status of both experiments, the recent upgrades to HAYSTAC for phase II, and the ongoing advancements of these exciting searches for physics beyond the standard model.
Neutrinos: a Unique Probe to Uncover the Secrets of Nature
Matteo Agostini, Technical University Munich
Neutrinos play a key role in our life. They are deeply involved in many particle and nuclear physics processes, from the microscopic world of subatomic particles till the evolution of entire galaxies. They can travel billions of light years, flying through planets and stars without interacting, and are thus unique probes to study our Universe. They are also a portal to uncover the fundamental laws of particle physics as some of their properties — e.g. their masses — cannot be explained with our current model and require new theories. In this talk I will discuss the experimental efforts to study the Sun with the BOREXINO experiment and the origin of neutrino masses with the GERDA and SOX projects.
Searches for New Physics at the Edge of Absolute Zero
Jonathan Ouellet, Massachusetts Institute of Technology
Why is there something in the universe instead of nothing?
What is the nature of the so-called Dark Matter that constitutes some 85% of the matter content of the universe?
These are two questions that each bring together physics on the largest of observable scales with the behavior of particles on the smallest of scales. Why matter formed and what caused it to cluster and form the galaxies and stars that we see in the universe are among the most fundamental open questions in physics today. And the answers may lie in understanding the breakdowns of the Standard Model. In this talk I will discuss the search for Neutrinoless Double Beta Decay — a lepton number violating decay that could help explain the matter-antimatter asymmetry of the Universe – and describe the CUORE experiment, a ton scale bolometric detector operating close to absolute zero, which searches for this decay. I will then discuss the axion and its reemergence as a leading contender to explain the Dark Matter abundance. I will then describe a new experimental program that we have started at MIT, in collaboration with UNC, to discover ADM called ABRACADABRA and present the first results from the ABRACADABRA-10 cm prototype.
Shedding ‘Nu’ Light on the Nature of Matter: The Search for Majorana Neutrinos
Julieta Gruszko, Massachusetts Institute of Technology
Why is the universe dominated by matter, and not antimatter? Neutrinos, with their changing flavors and tiny masses, could provide an answer. If the neutrino is a Majorana particle, meaning that it is its own antiparticle, it would reveal the origin of the neutrino’s mass, demonstrate that lepton number is not a conserved symmetry of nature, and provide a path to leptogenesis in the early universe. To discover whether this is the case, we must search for neutrinoless double-beta decay, a theorized process that would occur in some nuclei. By searching for this extremely rare decay, we can explore new physics at energy scales that only existed in the seconds following the Big Bang.
Detecting this extremely rare process, however, requires us to build very large detectors with very low background rates. Experiments using germanium detectors, like the MAJORANA DEMONSTRATOR, which is currently running, and LEGEND-200, which is moving forward quickly, are a promising strategy to explore lifetimes of up to 1028 years. The current generation of experiments have achieved the lowest backgrounds of any technique, and have a clear path forward to move to the ton-scale. I’ll present recent results from the DEMONSTRATOR, an update on LEGEND-200’s progress, and prospects for LEGEND-1000.
Reaching lifetimes beyond 1028 years, however, will require new techniques and kiloton-scale detectors. NuDot is a proof-of-concept liquid scintillator experiment that will explore new techniques for isotope loading and background rejection in future detectors. I’ll discuss the progress we’ve already made in demonstrating how previously-ignored Cherenkov light signals can help us distinguish signal from background, and the technologies we’re developing with an eye towards the coming generations of experiments.
Measuring and modeling scattered light for quantitative contrast of nanoscale tissue structure
Jeremy Rogers, University of Wisconsin-Madison
Diffuse light scattering in tissue is often considered problematic for imaging because it limits depth and contrast in many imaging modalities. However, scattered light carries information that can be used to quantify tissue structure at the nanoscale and develop new sources of image contrast. Exploiting scattered light contrast requires development of instruments for detailed characterization of tissue scattering, computational modeling, and customized imaging instruments. The sensitivity of scattered light to subtle differences in cellular and extracellular structure provides advantages in applications ranging from low cost cancer screening to development of new sources of quantitative contrast in retinal imaging.
Using a knowledge-in-pieces resources framework to organize our knowledge of learning in physics
Michael Wittmann, The University of Maine
As a physicist who leaned toward theory, I can’t help but be interested in the theories of education research and how they help us understand teaching and learning. One theory, the knowledge-in-pieces resources framework, describes small-grain ideas or procedures which are useful when solving a problem. I will describe several examples of the ways that the resources framework can help us analyze content knowledge and reasoning in physics. Topics include mechanical wave propagation and superposition, the use of mathematical integration in an intermediate mechanics course, and middle school teacher knowledge of students’ ideas about energy. Empirical settings have included the analysis of written data, the modeling of student discourse during problem solving, and ethnographic video data gathered when I was a participant in the teacher professional development community being studied. The breadth of the model’s applicability suggests its value in education research as a whole and in physics education research in particular, letting us model the fascinating and curious events that happen in our classroom.
Upcoming Spring 2019 Colloquia
Nuclear Structure and the search for neutrinoless doublebeta decay (0νββ): A case study of 72,76Ge
Akaa Daniel Ayangeakaa, United States Naval Academy
The observation of neutrinoless double-beta decay (0νββ) would simultaneously demonstrate the Majorana nature of the neutrino and provide experimental access to its absolute mass scale. Over the last decade, wavefunction contributions for leading (0νββ) candidates have been probed in a campaign of experiments utilizing transfer reactions to determine nucleon occupancies in a consistent way. While these studies have provided a great deal of information for comparison with theory, especially on contributions to the nuclear wavefunctions from competing orbitals, they lack sensitivity to the collective and shape degrees of freedom which are shown to be an integral component of the structure of parent-daughter nuclei relevant to 0νββ. In this talk, I will present results from high-precision Coulomb excitation measurements aimed at studying the various collective shape degrees of freedom and associated phenomena. The talk will focus primarily on the electromagnetic properties of low-lying states in 72,76Ge which were investigated via multistep Coulomb excitation using the advanced gamma-ray tracking array, GRETINA, and the charged-particle detector, CHICO2. The influence of the axial asymmetry parameter on the shape of these nuclei along with the results of multiconfiguration mixing calculations carried out within the framework of the triaxial rotor model will be highlighted. Most importantly, new experimental evidence characterizing the precise nature of triaxial deformation in 76Ge will be presented. The results will also be compared with state-of-the-art shell model calculations and recently obtained (n,n’γ) data, with emphasis on demonstrating the importance of nuclear deformation in determining the nuclear decay matrix elements relevant to neutrinoless double-beta decay (0νββ).
MRI illuminated by Gamma Rays
Wilson Miller, University of Virginia
Most medical imaging modalities have roots in old-fashioned nuclear physics. Magnetic Resonance Imaging (MRI), which is based on the spin dynamics of oriented nuclei, provides exquisite spatial and spectral resolution plus a rich variety of contrast mechanisms for visualizing disease states in the human body. Nuclear Imaging, which uses gamma cameras to detect energetic photons emitted during nuclear transitions, allows tracking of small quantities of radioactive tracers that seek particular disease targets within the body. My research group is developing what we hope will become a new medical imaging modality, that combines the spatial/spectral resolution of MRI with the detection sensitivity of nuclear imaging. This new modality, which we refer to as Polarized Nuclear Imaging, takes advantage of the fact that nuclear isomers with spin > ½ emit gamma rays in a spatially anisotropic pattern with respect to their spin orientation. The result is a fundamentally new imaging technique with some surprising properties. In this talk, I will describe the evolution of this (potentially) promising new imaging modality, from its origins in old-fashioned nuclear physics to the significant practical challenges that will ultimately determine whether its promise is ever fulfilled.
Emergence of Mass in the Standard Model
Craig D. Roberts, Argonne National Laboratory
Quantum Chromodynamics (QCD), the nuclear physics part of the Standard Model, is the first theory to demand that science fully resolve the conflicts generated by joining relativity and quantum mechanics. Hence in attempting to match QCD with Nature, it is necessary to confront the innumerable complexities of strong, nonlinear dynamics in relativistic quantum field theory. The peculiarities of QCD ensure that it is also the only known fundamental theory with the capacity to sustain massless elementary degrees-of-freedom, gluons (gauge bosons) and quarks (matter fields); and yet gluons and quarks are predicted to acquire mass dynamically so that the only massless systems in QCD are its composite Nambu-Goldstone bosons. All other everyday bound states possess nuclear-size masses, far in excess of anything that can directly be tied to the Higgs boson. These points highlight the most important unsolved questions within the Standard Model, namely: what is the source of the mass for the vast bulk of visible matter in the Universe and how is this mass distributed within hadrons? This presentation will provide a contemporary sketch of the strong-QCD landscape and insights that may help in answering these questions.
Andrea Shindler, Michigan State University
Christoph Baranec, University of Hawaii