Events During the Week of April 28th through May 5th, 2024
Monday, April 29th, 2024
- Plasma Physics (Physics/ECE/NE 922) Seminar
- “Metastability of stratified magnetohydrodynamic equilibria and their relaxation”
- Time: 12:00 pm - 1:15 pm
- Place: 1227 Engineering Hall
- Speaker: David Hosking, Princeton University
- Abstract: Astrophysical, space and fusion plasmas frequently exhibit explosive releases of energy. Motivated by such events, I consider in this talk the nonlinear stability of stratified magnetohydrodynamic equilibria to interchanges of straight magnetic-flux tubes. I demonstrate that, even under this restricted class of motions, plasma equilibria can be linearly stable while nonlinearly unstable, i.e., metastable. When destabilized, they can release their stored energy explosively. I show that the available energy with respect to interchanges can be determined accurately by solving a combinatorial optimization problem. The states with least energy are, to good approximation, the final states reached by simulations of the relaxation of metastable equilibria, provided that turbulent mixing is suppressed by viscosity. To predict the result of fully turbulent relaxation, I construct a statistical mechanical theory based on the maximization of Boltzmann's mixing entropy. This theory is analogous to the Lynden-Bell statistical mechanics of stellar systems and collisionless plasmas. The theory reproduces well the results of numerical simulations for sufficiently large initial perturbations to the metastable equilibrium.
- Host: Prof. Vladimir Zhdankin and Prof. Carl Sovinec
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Physics Potential at a future Muon Collider
- Time: 4:00 pm - 5:00 pm
- Place: 5310 Chamberlin Hall
- Speaker: Cari Caserotti, MIT
- Host: Sridhara Dasu
Tuesday, April 30th, 2024
- Preliminary Exam
- Modeling Solar Neutrino Flavor Evolution with Data Assimilation
- Time: 11:00 am - 1:00 pm
- Place: 5280 Chamberlin;
- Speaker: Caroline Laber-Smith
- Abstract: This talk will cover the application of statistical data assimilation (SDA) techniques to solar neutrinos in two cases. Statistical data assimilation is an inference method that incorporates system dynamics from theory to supplement sparse measurements. Solutions are found by minimizing deviation from both measurements and model dynamics and tested based on their predicted results outside of the measured region. We used this technique to model neutrino flavor evolution throughout the sun, starting from pure electron flavor at the center and undergoing Mikheyev-Smirnov-Wolfenstein (MSW) resonance as it travels outwards.
This is the first application of SDA to solar neutrinos using real data - measurements of Boron-8 solar neutrino flavor recorded by the Borexino and Sudbury Neutrino Observation (SNO) experiments were used to constrain neutrino flavor towards the edge of the sun. In the first case, we used this data as a test of the technique. We performed this optimization procedure with multiple energy bins matching the observations from the Borexino and SNO experiments separately. With both sets of measurements, we found that incorporating MSW resonance into the flavor evolution dynamics produces results consistent with the observations.
In the second case, we introduced parameter estimation by allowing the procedure to vary the matter potential inside the sun. As a test of adiabaticity, we used two different monotonically decreasing models of the matter potential as a function of radius. For each model, the potential was held fixed at the edge of our zone of inference to match the standard solar model, while the value at the core of the sun was used as a varying parameter. For both models, we found that a core potential between 0.025 and 0.030 per kilometer produces results most consistent with observed neutrino fluxes. - Host: Baha Balantekin
- Wisconsin Quantum Institute Seminar
- Nano-Photonic Emitters for the “Quantum Age”: where imperfections lead to opportunities
- Time: 3:30 pm - 5:00 pm
- Place: Discovery Building, DeLuca Forum
- Speaker: Evelyn Hu, Harvard University
- Abstract:
Although we usually assume that a "perfect" material is required to produce the best emitters for nano-optical devices, defect states in wide bandgap semiconductors are defining a new frontier for quantum information technologies, offering correlated spin-photon information. Numerous materials platforms have been explored, including single crystal diamond, SiC and Si: ultimately these defect qubits will need to satisfy quantum systems-level requirements for coherence, brightness, and equivalence of states.
This talk will introduce some building-block devices for the evaluation of candidate defect qubits, with a focus on Silicon Vacancies in 4H-SiC. Nanobeam photonic crystal cavities serve as both exquisitely sensitive optical amplifiers [1], as well as "nanoscopes" that allow us to better understand the local environment of the silicon vacancies, interactions with proximal defects and pathways to better processing and control of the defects [2].
Forming defects directly into cavities by "Laser Writing" allows more rapid feedback of optimal defect formation conditions [3]. Embedding G-center defects in Si, within PN diodes allows a dynamic assessment of processing conditions and fine-tuning of defect properties [4]. In aggregate, these techniques help to build the foundational understanding to take defect qubits to the “next steps” in implementing new quantum information technologies.
[1] Bracher, David O., Xingyu Zhang, and Evelyn L. Hu. "Selective Purcell enhancement of two closely linked zero-phonon transitions of a silicon carbide color center." Proceedings of the National Academy of Sciences 114.16 (2017): 4060-4065.
[2] Gadalla, Mena N., Andrew S. Greenspon, Rodrick Kuate Defo, Xingyu Zhang, and Evelyn L. Hu. "Enhanced cavity coupling to silicon vacancies in 4H silicon carbide using laser irradiation and thermal annealing." Proceedings of the National Academy of Sciences 118, no. 12 (2021): e2021768118.
[3] Day, Aaron M., Jonathan R. Dietz, Madison Sutula, Matthew Yeh, and Evelyn L. Hu. "Laser writing of spin defects in nanophotonic cavities." Nature Materials (2023): 1-7.
[4] Day, Aaron M., Madison Sutula, Jonathan R. Dietz, Alexander Raun, Denis D. Sukachev, Mihir K. Bhaskar, and Evelyn L. Hu. "Electrical Manipulation of Telecom Color Centers in Silicon." arXiv preprint arXiv:2311.08276 (2023).This event starts at 3:30pm with refreshments, followed at 3:45pm by a short presentation by Chengyu Fang (Mikhail Kats group), titled “Scalable passive optical masks that enable one- and two-species atom-trap arrays”. The invited presentation starts at 4pm.
- Host: Mikhail Kats
Wednesday, May 1st, 2024
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Expanding Horizons: Novel Strategies in low mass BSM Physics Exploration with CMS
- Time: 4:00 pm - 5:00 pm
- Place: 5310 Chamberlin Hall
- Speaker: Abhijith Gandrakota, FNAL
- Abstract: In the pursuit of Beyond the Standard Model (BSM) physics, the CMS experiment has employed unconventional techniques to uncover elusive phenomena. This presentation delves into three pivotal aspects of this effort during LHC Run-2 and the forthcoming Run-3 phases. Firstly, through the innovative use of Data Scouting in the search for low mass multijet resonances. Through this approach, we not only maximize sensitivity but also push the boundaries of traditional analysis methods. Next, we introduce Gaussian Processes as a powerful tool in BSM searches, with a significant ease of use and enhancing our ability to discern subtle signals amidst background processes. Finally, we turn our gaze towards the future. As we approach LHC Run-3, a critical facet of our strategy involves the revamping of the Level-1 trigger system. By incorporating anomaly detection techniques, we aim to elevate sensitivity to low mass resonances, unlocking new realms of discovery. This multifaceted approach, weaving together Data Scouting, Gaussian Processes, and L1 trigger innovation, showcases the CMS experiment's commitment to pushing boundaries and charting a course towards groundbreaking discoveries in BSM physics.
- Host: Sridhara Dasu
Thursday, May 2nd, 2024
- Thesis Defense
- A SEARCH FOR A STABLE SIX-QUARK BOUND STATE IN P-P COLLISIONS AT √ S = 13 TEV IN PARKED 2018 DATA AT CMS AND A STUDY OF THE AGING OF CATHODE STRIP CHAMBERS IN HIGH RADIATION ENVIRONMENTS.
- Time: 9:30 am - 11:30 am
- Place: 5280 Chamberlin Hall
- Speaker: Wren Vetens, Physics PhD Graduate Student
- Abstract: A search for a Standard Model dibaryonic dark matter candidate being produced in 13 TeV proton-proton collisions and annihilating with a neutron in the beam-pipe of the CMS detector is described herein. The search is to conducted in over 230 billion collisions collected in 2018 by the CMS detector, targeting the strange neutral hadrons that would be produced in such an annihilation. A custom vertex reconstruction is used, and a multivariate discriminator is trained to distinguish between the signal and a combinatorial background. Additionally, results from a study of the aging of detector components in Cathode Strip Chambers in high radiation environments with reduced Carbon Tetrafluoride gas mixtures are also presented.
- Host: Kevin Black
- Astronomy Colloquium
- Exploring Exoplanets in the Era of JWST and Beyond
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Knicole Colon, NASA's Goddard
- Abstract: We are in an extraordinary era of exoplanet science. This is thanks in great part to the number of current and upcoming facilities that are designed to enable the discovery of exoplanet systems or provide detailed characterization of exoplanets and their host stars across a range of ultraviolet to infrared wavelengths. In particular, the James Webb Space Telescope (JWST), which successfully launched in late 2021, is the premier space-based facility for near- and mid-infrared astronomy over 0.6-28.5 microns. The 6.5-meter telescope is specifically equipped with four state-of-the-art instruments that include capabilities for imaging, spectroscopy, and coronagraphy. JWST is providing unprecedented sensitivity enabling detailed studies of both transiting and directly-imaged exoplanets and their atmospheres. In this talk, I will review key exoplanet science results achieved so far with JWST and present results from some of our ongoing Cycle 1 and 2 programs to study giant and rocky transiting planets. I will then provide a look ahead at one of the next exciting exoplanet observatories that is planned to launch next year: a new SmallSat mission called Pandora that is being led out of NASA’s Goddard Space Flight Center and that is designed to study the impact of star spots on the spectra of exoplanet atmospheres. Together, observatories like JWST and Pandora are poised to re-write exoplanet textbooks for years to come.
- Host: Ke Zhang
- Physics Department Colloquium
- Frontiers in Neutrino Astronomy
- Time: 3:30 pm - 4:30 pm
- Place: 2103 CH
- Speaker: John Beacom, Ohio State University
- Abstract: tba
- Host: Baha Balantekin
Friday, May 3rd, 2024
- Academic Calendar
- Last Spring Semester class day
- Abstract: *Note: actual end time may vary.* URL:
- Thesis Defense
- A Study of Magnetized Plasma Turbulence in the Nonrelativistic and Relativistic Regimes
- Time: 2:00 pm
- Place: Sterling 1313;
- Speaker: Cristian Vega, Physics Graduate Student
- Abstract: Turbulence is ubiquitous in space and astrophysical plasmas and is believed to play an important role in particle heating and nonthermal acceleration. These plasmas are commonly threaded by an external magnetic field imposed by the object they surround (e.g., planet, star), making magnetized plasma turbulence a problem of significant interest. In this thesis, we use numerical simulations to study two relatively unexplored regimes of magnetized plasma turbulence, viz., the sub-electron inertial scale in nonrelativistic low electron beta plasmas and both the magnetohydrodynamic and kinetic scales in relativistically hot plasmas. Phenomenology is used to model the energy distribution of turbulent fluctuations and particles.
In the nonrelativistic regime studied, energy dissipation is seen to be strongly intermittent, concentrating on electron-scale current sheets. A few of these current sheets exhibit signatures of electron-only reconnection.
The particle energy probability density function in the relativistic regime displays a nonthermal tail of ultrarelativistic particles that goes from power-law-like to log-normal as the guide field is increased. We propose that this can be understood in terms of the acceleration mechanism that dominates in each case. Also noteworthy is the observed intermittency in the spatial distribution of ultrarelativistic particles. - Host: Stas Boldyrev
- Physics Department Colloquium
- The future of particle physics
- Time: 3:30 pm - 4:30 pm
- Place: 2241 Chamberlin Hall
- Speaker: Prof. Hitoshi Murayama, UC-Berkeley
- Host: Sridhara Dasu
Saturday, May 4th, 2024
- Academic Calendar
- Study day
- Abstract: *Note: actual end time may vary.* URL:
Sunday, May 5th, 2024
- Academic Calendar
- Exams
- Abstract: *Note: actual end time may vary.* URL: