Rosi Reed

Associate Professor

Lehigh University

Department of Physics

Host: Renee Fatemi

Title: Golden Age of Jet Tomography in Heavy Ion Collisions: The Evolution of Jets as Probes of the Quark Gluon Plasma

Abstract: The strong nuclear force, or quantum chromodynamics (QCD), remains one of the most enigmatic of the four fundamental forces of nature due to its rich structure and many emergent properties. The collision of heavy ions at ultra-relativistic speeds gives rise to a remarkable medium known as the quark gluon plasma (QGP). In this extreme state of QCD matter, protons and neutrons dissolve into partons - quarks and gluons - creating a nearly perfect liquid.  A fundamental question is whether quasi-particles exist in this medium, given the incredibly low viscosity over entropy ratio.  Answering questions regarding the evolution of the QGP structure, and the connection to QCD, requires probes with extremely small spatial resolution. Enter the particle jets created in high momentum transfer parton-parton collisions. These jets, produced early in the heavy-ion collision evolution, traverse the newly formed QGP and lose energy in a process called jet quenching, which modifies the final state properties of the resultant jets.  Understanding the mechanisms of jet quenching will allow the determination of QGP transport coefficients and thus lead to a better understanding of QCD.  The path-length dependence of the jet energy loss is one way to better understand the underlying mechanisms, though it has proven challenging to derive explicit values for the path-length dependence from experimental data.  We can gain critical insights into the nature of the QGP at both the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), to determine the temperature dependence, and system-size dependence of many jet observables.  In this presentation, I will discuss the latest Solenoidal Tracker at RHIC (STAR) experimental jet results, including a new measurement of the azimuthal asymmetry of jets in Ruthenium and Zirconium collisions, and compare these results with similar results from the LHC experiments, as well as the potential outlook for measurements with the newly built sPHENIX detector.  I will compare these results to recent advances in theory and connect them to other heavy ion jet measurements such as photon jet correlations and measurements of the structure of the jets themselves.

Prof. Robert Stamps

Department of Physics and Astronomy

University of Manitoba

Host: Lance DeLong and Todd Hastings

Title: Spin Vision: Using Artificial Spin Ice to Study Complex Systems

Abstract: Artificial Spin Ice is the name given to a class of metamaterials that are used as models for frustrated systems. In these models, frustration is introduced through competing interactions in a mesoscopic-scale array of interacting particles. Their experimental realization using nanomagnets as the interacting particles was first demonstrated in 2006 and opened a new field of study for frustrated systems. [1] As models in experiment, Artificial Spin Ice facilitate detailed observation in real time with high spatial resolution of complex out of equilibrium dynamics and thermodynamic processes. This flexibility underwrites their use in fundamental studies of a variety of nonlinear dynamics and ordering phenomena in low dimensions. 

Recent advances in fabrication now enable creation of complex two- and three-dimensional structures that have opened new possibilities for structural design and exciting new potentials for application in practical devices. [2] In this talk, a new cross-discipline direction for research that can benefit from Artificial Spin Ice models is explored. Motivated by studies of neural network models used in the analysis of experiments on primate vision, [3,4] a new type of three-dimensional Artificial Spin Ice geometry is proposed for implementation of a biologically plausible neuroscientific model called ‘active inference’. [5] Cast in the form of nanomagnetic spin geometries that can be studied experimentally, the approach can be used to facilitate a physics-based understanding of how complex systems might spontaneously generate a type of Bayesian filtering.

To achieve this, novel mechanisms for the control of magnetic states and ordering processes using three-dimensional geometries are required and different strategies are discussed. [6,7] A rudimentary ‘smart ASI’ is described whose design is based on state optimization principles assumed in some models used to describe general neurological processes.

1. RF Wang et al., Nature 439, 303 (2006).
2. SH Skjærvø, CH Marrows, RL Stamps, LJ Heyderman, Nature Reviews Physics 2, 13 (2020).
3. M Falconbridge, RL Stamps, DR Badcock, Neural Computation 18, 415 (2006).
4. M Falconbridge, RL Stamps, M Edwards, DR Badcock, i-Perception (in press).
5. RA Adams, E Aponte, L Marshall, KJ Friston, J. Neuroscience Methods 242, 1 (2015).
6. VM Parakkat, GM Macauley, RL Stamps, KM Krishnan, Physical Review Letters 126, 017203 (2021).
7. RB Popy, J Frank, RL Stamps, Journal of Applied Physics 132, 133902 (2022).

Tracy Webb

Associate Professor

Department of Physics

McGill University

Host: Yuanyuan Su

Title: Witnessing the evolution of the most massive galaxies in the densest regions of the universe

Abstract: An understanding of the formation and evolution of massive galaxies is a forefront goal of astrophysics today, observationally and theoretically. While we generally understand structure growth in the context of CDM hierarchical structure formation, and indeed this idea has been highly successful, new observations have shown that baryonic physics plays a key role. Indeed, the complex physics of galaxy-galaxy mergers, large scale gas cooling, and AGN feeding and feedback drive the evolution of massive galaxies. Given that at any given cosmic epoch the most massive galaxies tend to be found in over dense regions of the universe, one way to observationally find and study these systems is through a search for such peaks. In this talk I will describe, after introducing the field, an ongoing observational program to understand the evolutionary growth of massive galaxies that sit at the centres of giant galaxy clusters. With a focus on key systems and multiwaveIength data, I will argue that we do not yet fully understand how these giant beasts build up their stellar mass, but that progress is being made through efforts to push our observations to earlier epochs with new tools. 

Jeyhan Kartaltepe

Associate Professor

School of Physics and Astronomy

Rochester Institute of Technology

Host: Ryan Sanders

Title: TBA

Abstract: TBA

Prof. Jeanie Lau

Department of Physics

The Ohio State University

Host: Chunli Huang

Title: Flat Bands and Quantum Geometry in Flatlands

Abstract: In a flat band, the electronic interactions dominate, leading to emergent correlated phases such as superconductivity and charge density waves. The advent of flatlands, i.e. two-dimensional (2D) materials provide us with unprecedented opportunities to design and engineer flat bands via stacking, magnetic fields, and twisting. For flat bands in flatlands, quantum geometric contributions become important. To illustrate this, I will focus on superconductivity in twisted bilayer graphene, in which the slow Fermi velocity and the small charge density appear to invalidate conventional BCS equations and present a paradox. The paradox is resolved by our experimental demonstration that the superfluid stiffness is dominated by the quantum geometric contribution. We also find that the band velocity in this Dirac superconductor constitutes a new limiting mechanism for the critical current, analogous to a relativistic superfluid. Finally, I will also present on flat bands in suspended few-layer graphene, where gate tunable magnetism is observed. 

Nathaniel Craig

Associate Professor

Department of Physics

University of California, Santa Barbara

Host: Susan Gardner

Title: The “Who Ordered That” Collider

Abstract: In this talk, I’ll survey some of the major open questions in particle physics and make the case that they can best be addressed by a qualitatively new type of particle accelerator: a high-energy muon collider.  Recent progress on long-standing accelerator and detector challenges make such a collider a compelling successor to the LHC.

Prof. Martin Kruczenski

Department of Physics and Astronomy

Purdue University

Host: Anatoly Dymarsky

Title: Two applications of positivity to the theory of strong interactions (QCD)

Abstract: Although the fundamental description of the strong interactions is known, at low energy the theory is strongly coupled and calculations are more difficult as happens in many other areas of physics where perturbation theory does not apply.  On the other hand, recently, positivity conditions have been used to improve and obtain new non-perturbative results in quantum field theory, matrix models, and even classical mechanics.  Motivated by these, I will discuss how to use positivity in the context of gauge theories to find a gauge invariant formulation of lattice gauge theories in terms of Wilson loops, to compute certain low energy scattering amplitudes in two and four dimensions and even to find orbits in classical systems. I will also briefly discuss how these new applications have been fueled by new optimization algorithms developed for similar problems in engineering and finance.

Dr. Alec Tewsley-Booth

Postdoctoral Research Associate

Department of Physics and Astronomy

University of Kentucky

Host: Renee Fatemi and Tim Gorringe

Title: The Second Results from the Fermilab Muon g-2 Experiment

Abstract: On August 10th, 2023, the Muon g-2 Collaboration presented a new experimental value of the positive muon magnetic anomaly, a_μ = (g_μ - 2)/2. From this data set, the first analyzed since our release in 2021, we determine a_μ = 116592057(25) x 10^-11. This result dominates the new experimental world average, a_μ = 116592059(22) x 10^-11, which includes the 2021 result and the final result from Brookhaven in 2006. This talk will cover the experimental apparatus and analysis techniques used to produce the newest result, especially the improvements made that led to the factor of two improvement over the 2021 result. Additionally, we will cover the state of the theory and its tension with experiment, as well as the contributions from the University of Kentucky.

Yuanyuan Su

Assistant Professor

Department of Physics and Astronomy

University of Kentucky

Host: Gary Ferland and Tom Troland

Title: Studying galaxy clusters in multiwavelength, multiscale, and multidisciplinary

Abstract: As the largest gravitational bound systems in the Universe, galaxy clusters are one of the most important probes for testing the standard cosmological models. A typical galaxy cluster contains hundreds to thousands of member galaxies. The space between these galaxies is filled with hot and diffuse plasma -- the intracluster medium (ICM), which constitutes 90% of the baryonic mass and emits strongly in X-rays primarily through bremsstrahlung. ICM provides unique laboratories to study many astrophysical processes, such as the interaction between the hot baryons and the supermassive black hole, the growth of large scale structure, and the enrichment processes of the Universe. In this talk, I will present our recent discovery on galaxy clusters from its centers to the outskirts including the multiphase gas at the brightest cluster galaxies, bow shock in merging clusters, and the chemical composition of the ICM. Our work on active galactic nuclei in cluster member galaxies and machine learning applications will also be discussed. 

Prof. Susan Gardner

Department of Physics and Astronomy

University of Kentucky

Host: Brad Plaster

Title: QCD for New Physics Searches at the Sensitivity Frontier 

Abstract: 

Questions that drive searches for physics beyond the Standard Model  include the physical origin of the cosmic baryon asymmetry and of dark matter. Quark dynamics, as realized through the theory of quantum chromodynamics (QCD), can appear in these studies in very different ways. In this talk, I develop these possibilities explicitly, first describing the role of QCD in ultra-sensitive searches for new physics, particularly at low energies, and then turning to how its features could be exploited in describing the undiscovered universe, along with the essential observational and experimental tests that could confirm them.