Events at Physics

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Events During the Week of October 3rd through October 10th, 2021

Monday, October 4th, 2021

Plasma Physics (Physics/ECE/NE 922) Seminar
The onset of magnetic reconnection in collisional and collisionless plasmas
Time: 12:00 pm
Place: 2241 Chamberlin Hall
Speaker: Nuno Loureiro (MIT)
Abstract: Magnetic reconnection events are transient phenomena: a relatively quiescent plasma suddenly transitions to a reconnecting state where large amounts of magnetic energy are released. This sharp transition is known as the onset of magnetic reconnection. Analytical and numerical studies of reconnection often focus on assumed post-onset configurations and plasma parameters, by-passing not only the onset transition, but also the question of how such configurations came to be — and, perhaps more pertinently, of whether they are even physically realizable. For example, we now know that large-scale Sweet-Parker-like current sheets cannot form dynamically because they are subject to the super-Alfvénic plasmoid instability. Similar issues arise in collisionless plasmas, where the natural evolution of a given system leading to the formation of current sheets can trigger a variety of instabilities before such sheets reach electron scales. These notions imply that the onset of reconnection can be obtained by following the current sheet formation process and its transition from a stable to an unstable system. Moreover, I will argue that, because instabilities are inevitably triggered during the current sheet formation process, the (nonlinear) reconnection stage cannot be trivially decoupled from the current sheet formation stage; for example, the parameters characterizing the reconnection event may depend critically on the formation process and the instabilities that arise then. I will illustrate these issues both in the MHD and the kinetic regimes.
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Tuesday, October 5th, 2021

High Energy Seminar
Studies for a Low EMittance Muon Accelerator (LEMMA)
Time: 10:00 am - 11:00 am
Place: Video Recording:
Speaker: Manuela Boscolo & Marco Zanetti, INFN
Abstract: The concept of LEMMA uses a positron beam of about 45 GeV interacting on electrons on target. We will discuss the challenges, future plans and prospects of this proposal. We will present the accelerator scheme, with the optics and beam dynamics performed so far on the positron and muon beams. We will describe the challenges on the muon production target for a Multi-TeV muon collider in the 10^35 cm^-2 s^-1 luminosity range. An experimental program aiming to study the features of the process e+e- -> mu+mu- close to the production threshold, by using a positron beam of energy greater than 44 GeV on a solid target, is ongoing at the SPS CERN facility. The main goals are the precise measurement of the muon pair production rate and the emittance of the produced beam as a function of the center-of-mass energy and for different kind of targets. A summary of the 2018 beam test and the perspectives of the test beam planned for 2022 with an improved experimental setup will be presented. Video link:
Host: Sridhara Dasu
Presentation: LEMMA_seminar_6oct.pdf
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Thesis Defense
Instrumentation and Commissioning of the Prototype Schwarzschild-Couder Telescope Camera
Time: 1:00 pm
Place: 4274 Chamberlin Hall and Zoom:
Speaker: Leslie Taylor, Physics PhD Graduate Student
Host: Justin Vandenbroucke, Faculty Advisor
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Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
Mode-by-mode Relative Binning: Fast Likelihood Estimation for Gravitational Waveforms with Spin-Orbit Precession and Multiple Harmonics
Time: 2:00 pm - 3:00 pm
Speaker: Nathaniel Leslie, UC Berkeley
Abstract: Faster likelihood evaluation enhances the efficiency of gravitational wave signal analysis. We present Mode-by-mode Relative Binning (MRB), a new method designed for obtaining fast and accurate likelihoods for advanced waveform models that include spin-orbit precession effects and multiple radiation harmonics from compact binary coalescence. Leveraging the ``twisting-up'' procedure of constructing precessing waveform modes from non-precessing ones, the new method mitigates degrade of relative binning accuracy due to interference from superimposed modes. Additionally, we supplement algorithms for optimizing the choice of frequency bins specific to any given strain signal under analysis. Using the new method, we are able to evaluate the likelihood with up to an order of magnitude reduction in the number of waveform model calls per frequency compared to the previously used relative binning scheme, and achieve better likelihood accuracy than is sufficient for obtaining source parameter posterior distributions that are indistinguishable from the exact ones.
Host: Baha Balantekin
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Council Meeting
Time: 4:00 pm - 5:00 pm
Place: 2314 Chamberlin
Speaker: Mark Eriksson, UW-Madison, Department of Physics
Host: Mark Eriksson
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Wednesday, October 6th, 2021

Physics ∩ ML Seminar
Normalizing Flows for scientific applications
Time: 11:00 am - 12:15 pm
Place: Chamberlin 5280 (Zoom link also available for online participants who signed up on our mailing list)
Speaker: Uros Seljak, UC Berkeley
Abstract: Normalizing Flows (NF) are bijective maps from the data to a Gaussian (normal) distribution or viceversa. In contrast to other generative models they are lossless and provide data likelihood via the Jacobian of the transformation. I will first present a novel Sliced Iterative NF (SINF), which is based on Optimal Transport theory, achieving state of the art results in density estimation for small data samples and in anomaly detection applications in high energy physics. I will discuss its applications to Bayesian Inference and to Global Optimization problems, where it enables new methods of sampling and optimization, which have the potential to accelerate standard MCMC. In the second half of the talk I will present a Normalizing Flow for data structures with Rotational and Translational Equivariance (TRENF), which can be used for generative modeling and likelihood analysis of cosmological data. By training the data likelihood on the posterior this approach enables near optimal cosmological likelihood analysis, where information from all the data is optimally combined into a single number (likelihood) as a function of cosmological parameters. This method provides uncertainty quantification via the full posterior of cosmological parameters, which paves the way for a complete and optimal cosmological data analysis with Normalizing Flows.
Host: Gary Shiu
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Department Meeting
Time: 12:15 pm - 1:15 pm
Place: B343 Sterling
Speaker: Mark Eriksson, UW - Madison
Host: Mark Eriksson
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Particles Unknown
Time: 8:00 pm - 9:00 pm
Speaker: IceCube, IceCube
Abstract: IceCube is on PBS/NOVA!

Join the hunt for the universe’s most common—yet most elusive and baffling—particle.

Outnumbering atoms a billion to one, neutrinos are the universe’s most common yet most elusive and baffling particle. NOVA joins an international team of neutrino hunters as they try to capture an elusive fourth form of neutrino. Their results may force scientists to redraw their blueprint of the subatomic world, the Standard Model of physics, and change our understanding of how the universe works. (Premieres Wednesday, October 6 at 9 pm on PBS)
Host: Department
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Thursday, October 7th, 2021

Graduate Program Event
B.O.V. Presentation
Entrepreneurship in the Physical Sciences
Time: 12:00 pm - 1:00 pm
Place: 4274 Chamberlin Hall and/or
Speaker: Thomas Rockwell Mackie, Emeritus Professor, University of Wisconsin, Madison
Abstract: Academic physicists and the others in physical sciences have been important contributors for decades of ideas for commerce, including those resulting in new Wisconsin companies. Academic entrepreneurship enriches teaching, research, and is inherently service to the communities in which physics departments exist, the nation and even the world. There is a great difference between academic and commercial culture that must be understood to be successful and cultural differences will be highlighted throughout the lecture and will begin by describing the motivation, ideation, and creation of a physicist-entrepreneur, Albert Einstein, about a century ago. Particle accelerator developments during the 20th century provide examples of the cross-talk between academic physics and the medical industry. The 20th century being the Physics Century is highlighted by the story of the rise of the planet’s major entrepreneurial hub, Silicon Valley, surrounding Stanford. The rise of entrepreneurial biotechnology is heralding in the 21st century as the Biology Century, but there are still many exciting opportunities for products and services based on physics and biophysics yet to come.
Host: Prof. Kevin Black
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Astronomy Colloquium
Probing the primordial universe with high-resolution CMB and galaxy surveys
Time: 3:30 pm - 5:00 pm
Place: 4421 Sterling Hall, Coffee and Cookies at 3:30 pm, Talk starts at 3:45 pm
Speaker: Moritz Muenchmeyer, UW Madison
Abstract: The big bang can be viewed as a massive cosmological particle collider, whose output is the matter and radiation distribution that developed into the universe we observe today. By measuring the matter distribution of the universe more precisely, we can in principle learn more about the ultra-high energy physics of the early universe (inflation). However, extracting this primordial information is very difficult because of the complicated non-linear physics of structure formation. In this talk I will describe current and upcoming experiments, in particular focusing on secondary CMB anisotropies and galaxy survey data. I will show some recent ideas how their data can be used for primordial physics, and describe how modern computational methods from machine learning help to deal with non-linear physics.

We strongly encourage you to attend the colloquium in person. If that is impossible, it is available over zoom at the following link:

Host: Professor Ellen Zweibel
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Friday, October 8th, 2021

Graduate Introductory Seminar (Physics 701)
Quantum Hardware Simulations
Time: 12:05 pm - 12:55 pm
Place: 2241 Chamberlin
Speaker: Maxim Vavilov, UW Madison Department of Physics
Host: Sridhara Dasu
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Physics Department Colloquium
Glimpsing the Compositions of Sub-Neptune-Size Worlds
Time: 3:30 pm - 4:30 pm
Place: 2103 Chamberlin Hall
Speaker: Leslie Rogers, University of Chicago
Abstract: Sub-Neptune and super-Earth-size planets are a new category of astrophysical objects. Though absent from the Solar System, exoplanet surveys have revealed that they are a dominant outcome of planet formation found in abundance around other stars. The nature of these planets is not well understood. In the sub-Neptune size range a large variety of planet bulk compositions are a priori possible, including terrestrial super-Earths, mini-Neptunes with hydrogen-helium envelopes, and water-worlds with several tens of percent water by mass. In this talk, I will present recent results from my group aimed at understanding the nature and origin of these enigmatic sub-Neptune-size worlds and disentangling the relative contributions from various compositional scenarios to the observed population of planets.
Host: Ellen Zweibel
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