Department of Physics & Astronomy "Colloquia and Seminars" Series

Virtual 2020 - 2021 Program

Fridays @ 2:30 PM

Apr. 16^th, 2021 Dr. Cecille Labuda, Department of Physics & Astronomy, the University of Mississippi

   Spatial variation of the ultrasonic speed of sound and slope of attenuation in sheep brain

  Host: Dr. Dipangkar Dutta

  Abstract:

       Brain tissue is inhomogeneous due to its composition of different tissue types (gray and white matter), anatomical structures within the brain (such as the thalamus and cerebellum), and cavities in the brain (the ventricles). These inhomogeneities give rise to spatial variations of the ultrasonic speed of sound and attenuation as well as other ultrasonic properties. While the ultrasonic properties of mammalian brain, including the speed of sound and attenuation, have been reported throughout the literature from quite early on to the present, almost all of the reported data give aggregate values for the properties, that is, average values over a sample or tissue type are reported. In this work we report on the spatial variation of the speed of ultrasound and frequency slope of attenuation in sheep brain samples. The samples used in this study were 1-cm thick slices cut from whole sheep brain in three anatomic, the coronal, sagittal and transverse planes. Ultrasonic measurements were performed using broadband transducers with center frequencies of 3.5, 5.0, 7.5 and 10 MHz. The transducers were mechanically scanned to acquire signals from all locations on each slice and parametric images of these speed of sound and frequency slope of attenuation were produced. Spatial variation of the ultrasonic properties are clearly visualized in the parametric images. The images provide good representation of the anatomic structures, and white and gray matter are distinguishable in the parametric images as can be seen by comparison with photographic images.

Apr. 9^th, 2021 Dr. M.P. Anantram, Department of Electrical and Computer Engineering, University of Washington

   Electron Flow in DNA – Applications to disease detection and electronics

  Host: Dr. Prabhakar Pradhan

  Abstract:

       The four building blocks of DNA A, T, C, and G have unique ionization potentials. As a result, a sequence of these nucleotides in naturally occurring DNA sequences have unique electrical properties. After an introduction to DNA electronics, I will focus on our computational models and predictions for the electrical properties of DNA. Our approach uses a combination of Green's function method, quantum chemical calculations, and semiclassical molecular dynamics. We show that with sufficiently short sequences, it is possible to differentiate between single nucleotide mismatches in E. Coli, which code for diseases. We also envision DNA heterostructures' manufacturing with unique electronic properties representing devices including quantum wells and barriers. The efficacy of quantum mechanical wave interference in these devices is studied through computational experiments, and the results are encouraging. It turns out that suitably designed sequences can have a current contrast of close to one hundred, thus, opening the possibility to make read-only memory devices via DNA nanotechnology.

Collaborators: Apart from students in my group, Prof. Emre Oren and Busra Demir of TOBB University and Prof. Sunil Patil of Institute of Science.

Apr. 2^nd, 2021 No Colloquium Due to Easter Break

  

Mar. 31^st, 2021$☆$ Dr. Caryn Palatchi, Department of Physics, University of Virginia

   Perspectives on Parity Violation Electron Scattering Experiments and Electron Beam Asymmetries

  Host: Dr. Lamiaa El Fassi

  Abstract:

       A broad program of parity-violation measurements in electron scattering (PVES) will constrain nuclear structure models as well as search for new BSM physics. This program is comprised of the recent PREX-II (Lead Radius Experiment) and CREX (Calcium Radius Experiment) measurements which ran in 2019 and 2020, the upcoming MOLLER (Measurement of a Lepton-Lepton Electroweak Reaction) experiment and future EIC (Electron Ion Collider) structure function measurements including those probing weak neutral current interactions. The aim of the PREX-II and CREX measurements is to map the weak charge distribution in nuclei, with implications for the equation of state of highly dense matter, neutron stars, and gravitational waves produced in neutron star collisions. MOLLER is a future PVES experiment searching for new neutral currents, providing an unprecedented precision on the electron weak charge and electroweak mixing angle. The EIC with its high luminosity, polarized lepton and hadron beams, variety of nuclear targets, and wide kinematic range will open the door to searches of BSM physics, including new neutral currents, at energies and luminosities beyond the reach of presently possible experimental efforts.
      One common critical challenge for all of these experiments is measuring, analyzing, and managing electron beam properties and helicity correlated asymmetries in the polarized electron beam. This talk will describe the development of the newly installed RTP Pockels cell system in the JLab injector source which enables this program of experiments. Its development serves as an example of benchtop innovation and invention required to meet the technical challenges posed by increasingly precise measurements that probe BSM physics. The summer 2019 run of PREX2 will be reviewed, including illustrative data analysis methods and management of beam asymmetries, the result on the neutron skin thickness of Pb-208, and demonstration of precise nm-level control of electron beam asymmetries.

Mar. 29^th, 2021$☆$ Dr. Sanghwa Park, Department of Physics & Astronomy, Stony Brook University

   Proton and its complex inner life

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Proton is one of the two building blocks of nuclei, and studying its structure and properties is of vital importance in our understanding of the universe. Although it has been almost a century since Ernest Rutherford named the positive hydrogen nucleus as the proton, our understanding of its structure is still incomplete. Some of the questions that have been of great interest in nuclear physics relate to the structure of the proton in terms of its constituents and how its properties emerge. Many high energy scattering experiments have made important discoveries and set milestones. In this talk, I will summarize the recent progress with particular focus on spin observables. I will conclude with the exciting physics opportunities coming up on the horizon.

Mar. 26^th, 2021 Dr. Zhenhua Tian, Department of Aerospace Engineering, Mississippi State University

   Acoustic tweezers for dynamic manipulation of objects across seven length scales

  Host: Dr. Kun Wang

  Abstract:

       Acoustic tweezers use modulated acoustic waves to form virtual tweezers that enable dynamic manipulation of a wide range of objects scaling in sizes from nanometers to millimeters. Recently, acoustic tweezers have garnered increased interest across many fields including biology, chemistry, and engineering, as they can perform contactless, label-free, biocompatible, and precise manipulation of various objects including exosomes, cells, embryos, zebrafish larva, droplets, etc. This talk will introduce the fundamentals of acoustic tweezers as well as some latest technologies. Several functionalities of acoustic tweezers will be discussed, including translating and patterning cells, bioprinting, characterizing mechanical properties of cells, localized disruption of a cell, delivering DNA into stem cells, programmable translation of droplets, in-vivo manipulation through skulls, patterning CNTs, and levitation of mm objects. Lastly, this talk will extend to some recent studies on using metamaterials and valley topological phononic crystals to reshape acoustic waves for enabling next-generation acoustic tweezers.

Mar. 24^th, 2021$☆$ Dr. Timothy Rinn, Physics Department, University of Illinois, Urbana-Champaign

   Experimentally Probing High Temperature QCD with Heavy Ion Collisions

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Relativistic heavy ion collisions enable the study of QCD at high temperatures. At these high temperatures, a state of strongly interacting nuclear matter called the Quark Gluon Plasma (QGP) can be formed where quarks and gluons are no longer confined. A variety of both strongly and electromagnetically interacting probes are valuable to understand the properties of the QGP. In this talk, I will focus on measurements using “jets”, narrow cones of high momentum correlated particles produced by the fragmentation and hadronization of a quark or gluon. The jet constituents, quarks and gluons, are expected to lose energy due to interactions with the QGP causing an effect known as jet quenching. I will discuss recent experimental jet results from ATLAS which provide key insight into the workings of this plasma. Additionally, I will highlight the exciting prospects for involvement and of future insights to be gained from the under construction sPHENIX detector and the planned Electron Ion Collider.

Mar. 22^nd, 2021$☆$ Dr. Wenliang Li, Physics Department, College of William & Mary

   Probing the Darkside of Proton: u-Channel Meson Production from Jefferson Lab to EIC

  Host: Dr. Lamiaa El Fassi

  Abstract:

       In the past decade, the most important development in nuclear physics has been the establishment of a data inspired theoretical (GPD) framework that offers the complete spacial and momentum information of quark-gluon constituents within the nucleon. Recent pioneering studies at Jefferson Lab have shown evidences on the extra degrees of freedom of proton wave function that is only accessible through the backward-angle meson production observables, and these cannot be described by the current GPD framework. In this colloquium, a brief overview of the theoretical and experimental efforts on studying this unseen proton structure will be given; later section will introduce a systematic program and the plan on further exploring backward-angle meson production from Jefferson Lab to the future Electron Ion Colliders.

Mar. 19^th, 2021 Dr. Elena Litvinova, Department of Physics, Western Michigan University

   Nuclear many-body problem and astrophysics

  Host: Dr. Anatoli Afanasjev

  Abstract:

       Challenges and recent progress of the nuclear many-body problem on the fermionic correlation functions are presented. The proposed developments are implemented numerically on the basis of the relativistic effective meson-nucleon Lagrangian and compared to the simpler models considered to be the state-of-the-art in nuclear structure calculations. The results obtained for medium-heavy nuclei, in comparison to available experimental data, show that the higher-complexity configurations are necessary for a successful description of both gross and fine details of the spectra in both high-energy and low-energy sectors.
       The approach confined by the leading ph⊗phonon configurations beyond the standard random phase approximation has been extended recently to the case of finite temperature for both neutral and charge-exchange nuclear response. The associated many-body correlations, which play a decisive role in the structural properties of atomic nuclei, are thus linked to the astrophysical processes occurring during star evolution. The r-process nucleosynthesis predominantly occurring in the neutron star mergers requires the precise knowledge of the radiative neutron capture and beta decay rates in neutron-rich nuclei, which can be extracted from the microscopic strength distributions in the neutral and (p,n) Gamow-Teller and spin-dipole channels. The electron capture rates in the core collapse supernovae are related to the respective (n,p) spectra, which are also covered by recent applications. The perspectives of a unified nuclear many-body framework for generating the astrophysical input are outlined.

Mar. 12^th, 2021 Dr. Elena Long, Department of Physics & Astronomy, University of New Hampshire

   Understanding the Nature of Matter with Polarized Targets

  Host: Dr. Dipangkar Dutta

  Abstract:

       Since the discovery of the proton in 1917, physicists have been studying its properties: Asking questions about the internal structure and external phenomena of this basic piece of matter. This past century has been working to build an understanding that begins at the most fundamental quark level, builds up to protons and neutrons, and describes how they come together to form the atomic nuclei that make up everything we see around us. In just the past few decades, our understanding of this internal structure of nucleons has been greatly increased thanks to developments of high-energy electron accelerators and spin-polarized targets. From the quark sea through the internal electric structure of nucleons and beyond, this colloquium will cover the discoveries that have given us our current understanding of matter and detail current and future developments being led by the UNH Nuclear Physics Group that will teach us more about the nature of matter.

  Mar. 5^th, 2021 Dr. Hatef Sadeghi, School of Engineering, Warwick University

   Quantum interference and its application in molecular electronics

  Host: Dr. Kun Wang

  Abstract:

       At the level of fundamental science, it has been shown recently that molecular wires can mediate long-range phase coherent tunneling with remarkably low attenuation over a few nanometers, even at room temperature. This makes it possible to use quantum interference to control electron transport through nanoscale junctions. In this talk I will discuss the basic concept of quantum interference in molecular junctions and its application in molecular electronics including molecular switching, sensing and energy harvesting devices.

Feb. 26^th, 2021 Dr. Robert Goldston, Department of Astrophysical Sciences, Princeton University

  The New Nuclear Arms Race, Its Dangers, and How to Turn it Around

  Host: Dr. Lamiaa El Fassi

  Abstract:

       The United States and Russia are engaged in the first phases of a new nuclear arms race. With the recent shredding of arms-control agreements, this race may proceed unfettered and could lead to unprecedented dangers to humanity. As scientists we are obliged to understand the dynamics of this race and its dangers, and to lead in averting the rush to oblivion.
       Dr. Goldston is a professor of Astrophysical Sciences at Princeton University and associated faculty with Princeton’s Program on Science and Global Security. His research interests include neutron-based methods to verify warheads for disarmament, non-invasive UF6 flow meters and neutron detectors to verify operation of gas-centrifuge enrichment plants, and robotic techniques to monitor areas for undeclared nuclear materials and activities. He serves on the Board of the Council for a Livable World and writes policy pieces for the Bulletin of the Atomic Scientists.

Feb. 19^th, 2021 Dr. Donna Pierce, Department of Physics & Astronomy, Mississippi State University

  Fragment Species in the Comae of Comets: Observations and Challenges

  Host: Dr. Lamiaa El Fassi

  Abstract:

       The optical spectrum of the gas in a cometary coma is dominated by emissions of atomic and molecular fragment species that arise through one or more processes from larger precursor molecular species released from the nucleus. Optical spectral transitions of these fragment species are frequently observed using various spectrographic techniques, as well as photometry with narrowband filters. However, the full nature of the production of many of these species is poorly understood. Complete understanding of the presence and spatial distribution of these species in a comet coma is complicated by several factors, including uncertainties in the photodissociation and photoionization lifetimes of larger species, the processes that could release species from dust grains, a lack of robust chemical reaction rates that are applicable to cometary conditions, lack of spectral data, and an incomplete understanding of outgassing from the nucleus itself. In this discussion, we will review various observations of the gas coma, the ways that fragment species are connected to the larger species released from a comet nucleus, and the immediate challenges that multiple observed species present for understanding the full chemistry of comets and their relation to the solar system and the interstellar medium.

Feb. 12^th, 2021 Dr. Doyl Dickel, Department of Mechanical Engineering, Mississippi State University

  Bridging Length Scales: Machine Learning of Density Functional Theory

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Density functional theory (DFT) has been the primary choice for solid-state physics calculations for the last 30 years due to its ability to efficiently and accurately solve a wide variety of electronic structure problems. However, its expensive scaling with respect to number of electrons makes it a poor choice to study systems of more than about 100 atoms. This makes it difficult to use DFT directly to address phenomena, particularly in solids, which require larger systems to simulate. Semi-empirical classical potentials have been used extensively for modeling at this higher length scale, but accuracy can suffer extensively compared to DFT and development times of potentials for new materials and alloys can be prohibitive.
       Machine learning provides a novel method for encoding the results of DFT at high accuracy using only a fraction of the computational time. The flexibility of artificial neural networks (ANNs) in particular has lent itself to reproducing DFT results to single meV/atom accuracy while operating on timescales comparable to classical MD formalisms. In this colloquium, I will present a procedure for generating machine learned interatomic potentials which reproduce DFT-level accuracy and are applicable to a variety of solid-state systems. While many of the results will be for ordinary metallic or ceramic systems, extensions to polymeric systems and to magnetic materials will also be discussed.

Feb. 5^th, 2021 Dr. Wencan Jin, Department of Physics, Auburn University

   Probing a ferro-rotational order by optical second harmonic generation

  Host: Dr. Kun Wang

  Abstract:

       A ferro-rotational order describes a ferroically ordered state of an axial vector moment that is invariant under both spatial inversion and time reversal operations. This order was first theoretically proposed to complete the classification of ferroics with vector order parameters, and now is the last remaining class to be revealed after the discoveries of ferro-toroidal, ferromagnetic, and ferroelectric orders. More recently, this order is suggested to exist in a good number of complex oxides, and is considered to be responsible for several novel phenomena including the type-II multiferroic order. In this talk, I will present our studies of the ferro-rotational order in a type-II multiferroic material RbFe(MoO4)2 using high sensitivity rotational anisotropy second harmonic generation (RA SHG). I will show that the higher order electric quadrupole (EQ) contribution to SHG has been exploited to investigate this inversion-symmetry-preserved ferro-rotational order. I will then reveal several physical properties of this ferro-rotational order including its symmetry, domain distributions, temperature evolutions, and conjugate coupling field. I will further discuss the significance of understanding this ferro-rotational order and the opportunity brought by high sensitivity EQ SHG.

W. Jin et al., Observation of a ferro-rotational order coupled with second-order nonlinear optical fields. Nat. Phys. 16, 42-46 (2020).

Jan. 29^th, 2021 Dr. Govind Menon, Department of Physics & Chemistry, Troy University

   Degenerate Electrodynamics and Blackhole Magnetospheres

  Host: Dr. Dipangkar Dutta

  Abstract:

       When the plasma energy density is significantly weaker than the electromagnetic energy density, the Maxwell field satisfies the additional constraint given by. This is the realm of force-free electrodynamics (FFE) and is the case for many astrophysical blackholes. I will discuss the mathematical structure behind force-free electrodymaincs and its connection to foliations of spacetime. The primary mechanism behind the observed jets from supermassive blackholes are attributed to FFE.

Jan. 22^nd, 2021 Dr. Alexandra Hui, Department of History, Mississippi State University

   How Scientists Listen: A History

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Hui’s research addresses the many ways in which how scientists listen to the world around them and how this auditory experience informs their science. She has closely examined the role of music in early psychoacoustic research from the nineteenth century, how graphic representation of bird sound shaped what early twentieth-century ornithologists heard, the use of large public surveys to establish an understanding of music as functional, to be applied to manipulate mood and behavior, and more. Threading these many historical studies, is an interest in the role of sound and the act of listening in the construction of sonic spaces, both perceptual and material. In particular, Hui is interested in how wilderness and nature, became local, real, and meaningful for individuals through their ears. And their ears, in turn, were centrally important to the development of modern conceptions of the environment (natural and built) and environmentalism. She will focus in this talk on both the broad social mechanisms and the individual sensory-perceptual processes through which new knowledge in the natural sciences, new devices, and new sounds were developed.

Jan. 15^th, 2021 Dr. Christine Aidala, Department of Physics, University of Michigan

   The Electron-Ion Collider: Tackling Quantum Chromodynamics from the Inside (of Protons and Nuclei) Out

  Host: Dr. Lamiaa El Fassi

  Abstract:

       The future Electron-Ion Collider (EIC) is a next-generation facility for the precision study of quantum chromodynamics (QCD), the theory of the strong nuclear force. The EIC will collide beams of polarized electrons with beams of polarized protons and light nuclei as well as unpolarized heavy nuclei, offering a wealth of new insights into the quark and gluon degrees of freedom within the nucleons and nuclei of everyday matter. It will be sited at Brookhaven National Laboratory, adding an electron accelerator to the existing Relativistic Heavy Ion Collider, and is expected to start taking data in 2030. A community of more than 1200 experimental, theoretical, and accelerator scientists from 34 countries is currently refining the accelerator and detector designs as well as the physics program for the facility.

Past Fall 2020 Semester's Colloquia/Seminars

Nov. 13^th, 2020 Mr. Ahmad Taninah, Department of Physics & Astronomy, Mississippi State University

  Covariant density functional theory: functionals and input for r-process modelling

  Host: Dr. Lamiaa El Fassi

  Abstract:

       Covariant density functional theory (CDFT) is a modern theoretical tool for the description of atomic nuclei. There are three major classes of covariant energy density functionals. These are meson exchange functionals with non-linear and explicit density dependencies as well as point coupling functionals without meson exchange. I will start from the consideration of basic features of CDFT and the propagation of statistical errors in the description of physical observables on moving to unknown regions. This will be followed by the discussion of parametric correlations existing in different classes of the functionals; their removal allows to reduce the number of independent parameters in the functionals to 5 or 6. In the second part of the talk, I will present the results of systematic investigation of the ground state and fission properties of even-even actinides and superheavy nuclei with proton numbers 𝑍=90−120 located between the two-proton and two-neutron drip lines. These results provide a necessary theoretical input for the modelling of the nuclear astrophysical r-process taking place in the mergers of neutron stars.

  Nov. 6^th, 2020 Dr. Hebin Li, Department of Physics, Florida International University

 Optical 2D Coherent Spectroscopy of Many-body Interaction and Correlation in Atomic Vapors

 Host: Dr. Gombojav Ariunbold

 Abstract:

       Many-body interaction and correlation in an atomic ensemble are fundamental in understanding collective and emergent phenomena in many fields such as cold atoms/molecules, optical atomic clock, semiconductor, and photosynthesis. Cold atoms/molecules provide a well-controlled system for studying many-body physics. On the other hand, rich structural and dynamic information about interatomic interaction and correlation can be found in atomic vapors at room or higher temperatures. Compared to cold atoms, a thermalized atomic vapor provides a broader range of mean interatomic separation and more atoms for experiments. Thermal motion also introduced many-body effects and dynamics that may not present in cold atoms and may be shared by natural processes in chemical and biologic systems. Experiments with thermalized atoms can complement studies in cold atoms/molecules for a full understanding of many-body interaction and correlation.
      I will present our recent studies of many-body interaction and correlation in potassium and rubidium atomic vapors by using a novel ultrafast spectroscopic technique – two dimensional (2D) coherent spectroscopy. This technique provides an extremely sensitive and background-free detection of interatomic dipole-dipole interactions even in a dilute gas that is usually considered ideal gas. Our results reveal effects of dipole-dipole interactions at a mean interatomic distance up to tens of micrometers, confirming the long-range nature of dipole-dipole interaction. The signal amplitude is measured at different atomic densities across five orders of magnitude, providing valuable data to compare with results from different theoretical models. By extending the experiment to higher-order excitation processes, 2D coherent spectroscopy can create and detect multi-atom Dicke states with two, three, four, five, six, and seven atoms. These multi-atom Dicke states can be further confirmed by the increasing dephasing rate with the number of atoms. The observation of scalable and deterministic multi-atom Dicke states in an atomic vapor has possible implication in fundamental many-body physics and quantum information science.

Oct. 30^th, 2020 Dr. Samantha Lawler, Campion College and the Department of Physics, University of Regina, Canada

 Planet 9 or Planet Nein? Discoveries in the Outer Solar System

 Host: Dr. Angelle Tanner

 Abstract:

      

The Outer Solar System Origins Survey (OSSOS) was a 5 year survey on the Canada-France-Hawaii Telescope that discovered over 800 new trans-Neptunian objects (TNOs) with some of the most precisely-measured orbits to date. OSSOS was designed to carefully track all possible observational biases, and account for these biases via Survey Simulator software that can be used to statistically test different TNO orbital distribution models. Accounting for all possible survey biases is particularly important for high-pericenter TNOs, which are only detectable for a small fraction of their orbit. High-pericenter TNOs have recently been in the news for showing an apparent clustering in their orbital distribution, which some propose is caused by an additional planet in the distant Solar System (popularly referred to as Planet 9). But is this apparent orbital clustering real? I will discuss the distribution of these hard-to-detect high-pericenter TNOs, as well as other interesting discoveries from the OSSOS survey, such as the orbital structure of resonances and implications for Neptune’s migration.

Oct. 23^rd, 2020 Dr. Philip Phillips, Physics Department, University of Illinois Urbana-Champaign

 Beyond BCS: An Exact Model for Superconductivity and Mottness

Host: Dr. Dipangkar Dutta

Abstract:

       High-temperature superconductivity in the cuprates remains an unsolved problem because the cuprates start off their lives as Mott insulators in which no organizing principle such a Fermi surface can be invoked to treat the electron interactions. Consequently, it would be advantageous to solve even a toy model that exhibits both Mottness and superconductivity. In 1992 Hatsugai and Khomoto wrote down a momentum-space model for a Mott insulator which is safe to say was largely overlooked, their paper garnering just 21 citations (6 due to our group). I will show exactly [1] that this model when appended with a weak pairing interaction exhibits not only the analogue of Cooper's instability but also a superconducting ground state, thereby demonstrating that a model for a doped Mott insulator can exhibit superconductivity. The properties of the superconducting state differ drastically from that of the standard BCS theory. The elementary excitations of this superconductor are not linear combinations of particle and hole states but rather are superpositions of doublons and holons, composite excitations signaling that the superconducting ground state of the doped Mott insulator inherits the non-Fermi liquid character of the normal state. Additional unexpected features of this model are that it exhibits a superconductivity-induced transfer of spectral weight from high to low energies and a suppression of the superfluid density as seen in the cuprates.

[1] https://www.nature.com/articles/s41567-020-0988-4.

Oct. 16^th, 2020 Dr. Anatoli Afanasjev, Department of Physics & Astronomy, Mississippi State University

 Extending the limits of the nuclear landscape via new physical mechanisms

 Host: Dr. Lamiaa El Fassi

 Abstract:

       What are the limits of the existence of nuclei? What is the highest proton number Z at which the nuclear landscape and periodic table of chemical elements cease to exist? How nuclear excitations affect the drip lines and physics of nuclei near it? In my presentation, I will focus on recent applications of covariant density functional theory to the nuclei at the limits of nuclear landscape and for the search of new physical mechanisms which would allow to expand these limits. First, I will discuss the physics of hyperheavy (Z> 126) nuclei and the role of toroidal and ellipsoidal nuclei in the extension of the nuclear landscape. Next I will consider the impact of the rotation both on the properties of the nuclei located near and beyond spin-zero neutron and proton drip lines and on the extension of nuclear landscape beyond these lines. The results of other on-going studies of the nuclei at the limits will also be discussed.

  Oct. 9^th, 2020 Dr. Jamie Tayar, Institute for Astronomy, Hawaii University

 Better Stars, Better Planets: Linking Stellar Physics to the Search for Habitable Worlds

 Host: Dr. Angelle Tanner

 Abstract:

       With the discovery of thousands of extrasolar planets in the past decade, the search is on to determine whether habitable planets like our earth are common or rare. However, most properties of extrasolar planets are measured relative to their host stars, so in many cases it is our lack of understanding of stars that limits this search. I will discuss current limitations on our understanding of the physics of stellar interiors, including convection and rotation, and what that means for our ability to model stars and accurately estimate stellar parameters. I will show that characterizing stellar variability and oscillations has vastly improved our understanding of stars in the past few years, and offers an opportunity to identify the best planets for future investigations of exoplanet habitability.

  Oct. 2^nd, 2020 Dr. Keith Baker, Physics Department, Yale University

 Quantum Entanglement in High Energy Physics

 Host: Dr. Dipangkar Dutta

 Abstract:

       Quantum entanglement can have observable effects in high energy physics, and its understanding may explain certain anomalies in the field. The relationship between quantum entanglement and an observed thermalization in particle production at the Large Hadron Collider, akin to thermal phenomena at the event horizon of black holes, is an example. The considerable amount of collected data at 13 TeV proton-proton collision energy enables systematic investigation of this physics, including even in the Higgs sector. Additional links between Quantum Information Science and particle physics at the energy and intensity frontiers, along with near-term future studies, will be presented.

Sept. 25^th, 2020 Dr. Jessica Arnold, Carnegie Institution for Science, Department of Terrestrial Magnetism & Army Research Lab

 Light beams on dust: a window into planetary systems

 Host: Dr. Chuji Wang

 Abstract:

       My work aims to improve characterizations of the materials in developing planetary systems and regoliths of airless solar system objects using light scattering and radiative transfer models. Debris disks are generated by the collision and disruption of planetesimals analogous to asteroids and comets in our own solar system, which produces micron-sized dust grains. Understanding the composition of the material within these extrasolar systems may provide insight into the planet formation process. As debris disks are typically too cold to produce key identifying silicate spectral features in thermal emission near 10 μm, scattered light in the visible and near infrared wavelength range is important for making compositional determinations. To interpret scattered light observations of debris disks we need to model the light scattering properties of the constituent dust, which depend on grain composition, size, and structure. I will present a model that uses scattering efficiencies for realistic grain shapes to retrieve the dust grain properties of the AU Microscopii debris disk. I will also show that dust grain shape has an effect on the predicted radiation pressure blowout size in debris disks. This has implications for both disk composition and minimum expected grain size.

Sept. 18^th, 2020 Dr. Gautam Rupak, Department of Physics & Astronomy, Mississippi State University

 Fate of the neutron-deuteron virtual state as an Efimov level

 Host: Dr. Lamiaa El Fassi

 Abstract:

       The emergence of Efimov levels in a three-body system is investigated near the unitarity limit characterized by a resonant two-body interaction. No direct evidence of Efimov levels is seen in the three-nucleon system since the triton is the only physical bound state. We provide a model-independent analysis of nucleon–deuteron scattering at low energy by formulating a consistent effective field theory. We show that virtual states evolve into shallow bound states, which emerge as excited triton levels as we drive the system towards unitarity. Even though we consider this specific system, our results for the emergence of the Efimov levels are universal.

Sept. 11^th, 2020$☆$ Dr. Kun Wang, Departments of Physics & Chemistry, Mississippi State University

 Controlling Quantum Transport at the Molecular Scale for Optoelectronics and Energy Applications

 Host: Dr. Keith Hollis

 Abstract:

       Molecules are the fundamental building blocks of any materials. Creating functional devices at the molecular scale and understanding the underlying physics and chemistry hold promise for developing smaller, faster, and more efficient nanodevices for applications in optoelectronics, energy conversion, and chemical/bio-sensing.
      In this talk, I will introduce my recent research in developing experimental tools to address challenges in probing and controlling charge and energy transport in molecular tunnel-junction devices. First, I will begin by showing how a single molecular diode and switch can be experimentally built and characterized (Nat Chem 2016). Second, I will introduce experimental observation of thermoelectric energy conversion at the molecular scale (Nat Nanotechnol 2018). Third, I will talk about our recent breakthrough in quantifying plasmonic hot carrier distribution via single molecule transport measurements (Science 2020).

  Sept. 4^th, 2020 Dr. Ketevi Assamagan, Brookhaven National Laboratory

 Using the Higgs boson to search for dark sector particles

 Host: Dr. Dipangkar Dutta

 Abstract:

       The discovery of the Higgs boson opens a new and rich experimental program that includes using the Higgs boson to search for new particles. In this talk, I will discuss searches for dark sector particles in the decays of the Higgs Boson.

Aug. 28^th, 2020 Dr. Mark Novotny, Department of Physics & Astronomy, Mississippi State University

 'Order amidst Disorder' in semi-regular, 'tatty', and atypically random buildable 'Quantum Dragon' nanodevices

 Host: Dr. Lamiaa El Fassi

 Abstract:

          

Shown are four nanodevices attached to leads. [These show a ball-and-stick model for a tight-binding Hamiltonian]. From the Schrödinger equation solution, an electron flux comes in from the left lead, undergoes scattering in the device, and is transmitted to the right lead with some probability. Both the ordered nanodevices (left) and the disordered nanodevices (right) have 100% electron transmission for all energies of the incoming electron! Thus in two probe electrical measurements all four are metallic … and in fact would have zero electrical resistance. How does this happen? What is a quantum dragon nanodevice? Just what does ‘tatty’ mean for nanodevices? These questions will be addressed.

Aug. 21^st, 2020 Dr. Catherine Ayuso, Department of Physics & Astronomy, Mississippi State University

 Exploring J/ψ production at the E906/SeaQuest and E1039/SpinQuest experiments: nuclear effects, Sivers gluon function and improved online monitoring

 Host: Dr. Lamiaa El Fassi

 Abstract:

       The E1039/SpinQuest experiment is a transversely polarized fixed target experiment at Fermi National Accelerator Laboratory seeking to explore the virtual-quark and gluon Sivers functions via the measurement of single spin asymmetries for a number of physics processes including J/ψ, ψ' and Drell-Yan production. The experiment employs a 120-GeV extracted proton beam colliding with transversely-polarized NH3 and ND3 cryogenic targets and its spectrometer is optimized to detect the oppositely-charged muon pair output of these processes. Given the center of mass energy of E1039, we expect J/ψ production to be primarily governed by gluon-gluon interactions and can thus serve as a good probe to measure asymmetries constraining the poorly known gluon Sivers function. In pursuit of this measurement, we are seeking to develop an advanced GPU-based multi-threaded framework that allows an efficient parallelization of the online data processing, which will facilitate prompt online reconstruction, optimizations, and robust data quality monitoring. This presentation will focus on the framework for this online monitoring software and report the status of the experiment, as well as previous J/ψ nuclear modification measurements from the experiment’s predecessor, the E906/SeaQuest experiment.

2020-2021 Committee