The first colloquium of spring 2026 will be a Town Hall to discuss the department’s achievements and goals, followed by a Q&A with faculty, staff, and students.

Note: Because of weather UT is following remote operations for February 2. This colloquium has been moved to Zoom.

Nature violates parity symmetry. Discovered almost 70 years ago, this phenomenon implies that the universe is “left handed.” Although we have a very successful theory, the Standard Model of Particle Physics, which agrees with scores of experimental tests, it includes parity violation in an ad hoc way. There are hints that the Standard Model should break down at very high energies, restoring parity symmetry. There are viable conjectures for how that might come about, and much of High Energy Physics tries to reach the energy scales where this breakdown might occur.

This talk describes a different approach, trading very high energy interactions for extremely precise measurements at lower energies. The MOLLER experiment at Jefferson Lab will measure parity violation in electron-electron scattering for which the Standard Model makes a precise prediction. Disagreement between experiment and theory at this level would indicate “new physics” at energies beyond the reach of current high energy collider facilities. After introducing the key concepts, I will describe the challenges of making this ultra precise measurement and the timeline for executing the experiment.

Below the geographic South Pole, the IceCube project has transformed one cubic kilometer of natural Antarctic ice into a neutrino detector. IceCube detects more than 100,000 neutrinos per year in the one to a million GeV energy range. Among those, we have isolated high-energy neutrinos originating beyond our Galaxy, with a flux that exceeds the extragalactic high-energy gamma-ray flux observed by astronomers in a similar energy range. With a decade of data, we have identified their first sources, which point to supermassive black holes at the centers of active galaxies powering the cosmic ray accelerators that produce high-energy neutrinos. Machine learning techniques eventually revealed that our own Milky Way emits neutrinos but, interestingly, it is not a prominent feature in the neutrino sky as it is in all wavelengths of light. We will also review the study of the neutrinos themselves, emphasizing oscillation measurements.

Magnons and phonons are collective excitations in crystals that often behave as independent quasiparticles when their mutual coupling is weak. When magnetoelastic coupling becomes strong, interactions between spin and lattice degrees of freedom can open gaps at band crossings and give rise to hybridized excitations known as magnon-polarons. Because such hybridized modes appear only when energy matching, symmetry compatibility, and microscopic coupling all align, their presence and momentum dependence provide a particularly sensitive probe of the underlying spin–lattice interactions.

In this talk, I will use the olivine-type silicate Co₂SiO₄ to illustrate how this physics plays out in a real material. I will begin by presenting inelastic neutron-scattering measurements that reveal a rich set of hybridized excitations involving magnons, phonons, and spin–orbit excitons. To understand these observations, I will introduce an effective spin Hamiltonian that captures the main features of the magnetic excitations and discuss density functional theory calculations that reproduce the phonon spectrum. Building on these microscopic descriptions, a symmetry analysis of the magnon and phonon modes reveals which excitations can hybridize and where in momentum space such coupling is allowed. This framework naturally leads to a minimal hybridization model that explains the observed avoided crossings and mode mixing, providing a unified picture of the hybridized excitation spectrum in Co₂SiO₄.

More broadly, this work establishes olivine-type oxides as a clean setting for studying magnetoelastic coupling and illustrates how combining dynamical measurements with symmetry-based modeling can reveal microscopic interactions that are difficult to access otherwise.

The magnetic moment of muon can be characterized by its gyro-magnetic factor $g$, which is numerically close to 2. Fermilab announced a new experimental result for muon $g-2$ on June 3, 2025.
The new result is consistent with the previous BNL measurement, but with about 4 times higher precision. For the Standard Model prediction, the recent theoretical muon $g-2$ white paper was released on May 27, 2025. The new theory result is consistent with the new experimental result, but is about 3 sigma larger than the previous theory white paper result, released on June 8, 2020. Two hadronic contributions, HVP (hadronic vacuum polarization) and HLbL (hadronic light-by-light), are the dominant sources of the theoretical uncertainty. The change in the central value is largely due to the many advances in lattice QCD calculations of these hadronic contributions, particularly the HVP contribution. In this talk, I will describe the theoretical determination of muon $g-2$ with focus on the lattice QCD calculations of the hadronic contributions.

Neutrinos provide a promising window to probe a wide range of fundamental physics. Neutrino related discoveries in the last two decades indicate that the answer to the most sought after question of why we live in a matter-dominated universe may be within reach. Although more than a trillion of neutrinos pass unnoticed through our bodies every second, they still remain largely mysterious. These ghostly little particles are notoriously difficult to detect given how rarely they interact with matter and require building immense and exquisitely sensitive detectors. The Deep Underground Neutrino Experiment (DUNE) is a next generation neutrino experiment at Fermilab and South Dakota in United States with primary goals of resolving the neutrino mass ordering and measuring the charge-parity violating phase, the indicator of a possible explanation for our matter dominated universe. DUNE will use the promising liquid argon time projection chamber (LArTPC) technology as it presents neutrino interactions with unprecedented detail. After briefly reviewing the current state of neutrino physics and open questions, this talk will describe the DUNE experiment along with the rich physics that it offers and its current status.

There will be no physics colloquium during spring break.

There will be no physics colloquium on March 16, 2026.

The weak force of nature uniquely allows quarks to change flavor, resulting in the transformation of nuclei known as nuclear beta decay. Currently, measurements of the weak mixing of quarks are in tension with the Standard Model’s description, a discrepancy referred to as the “Cabibbo Angle Anomaly.” As the simplest nucleus to undergo beta decay, the neutron has emerged as a system which can provide a competitive measurement and shine light on this anomaly if experimental uncertainties in the neutron dataset can be improved. The Nab experiment at the Spallation Neutron Source employs a novel and robust approach to improve decay correlation measurements by observing the full momentum phase space in neutron beta decay accessible above detection thresholds. The tight kinematic constraints from the experiment have recently been used to place first limits on a new hypothesized excited state of the neutron, suggested to address experimental disagreements in neutron lifetime measurements. In this presentation, I will describe the working principles of the experiment, present early results from first physics data-taking, and discuss the outlook for Nab and its upgrade pNAB (polarized Nab) to perform world-leading measurements of neutron decay correlations and improve our understanding of quark mixing in the weak interaction.

Living systems are driven far from thermodynamic equilibrium through the continuous consumption of ambient energy. This energy is invested in the formation of complex, internal macromolecular structures and diverse spatial and temporal patterns in chemical and mechanical activities, which in turn orchestrate cell phenotypes and behaviors. This self-organization is a result of a system’s tendency to maximize entropy production while maintaining order internally. However, a system that maximally dissipates energy can achieve high levels of organization and complexity, although this comes at the cost of low thermodynamic efficiency. Despite decades of research, little is known regarding the energetic principles and optimization strategies that constrain the dissipation of energy arbitrarily far from thermodynamic equilibrium. In this seminar, we explore energetic optimization, in studying the assembly of the cytokinetic ring, a complex structure that is an essential component of cellular reproduction and a defining aspect of living systems. Using the Xenopus Oocyte as a model system, we measure the production of entropy, as the cell approaches ring assembly and its first cell division. We demonstrate that en route to division, the production of entropy is maximized, but insofar as the overall system is subject to constraints of Onsager Reciprocity. Thus, in living systems, multiple energetic parameters are optimized simultaneously to promote and sustain life.

Quantum spin liquids—magnetic states characterized by long-range entanglement and fractionalized excitations—challenge the conventional description of antiferromagnets in terms of ordered moments and magnons. In this talk, I revisit the evolution of ideas about the antiferromagnetic ground state, from semiclassical order to resonating valence-bond constructions and parton descriptions with emergent gauge structure, highlighting how these frameworks reshape our understanding of magnetic excitations.

I then turn to the two-dimensional Dirac quantum spin liquid, a candidate realization of (2+1)-dimensional quantum electrodynamics with gapless Dirac spinons coupled to an emergent U(1) gauge field. A central question is how such a state responds to an external magnetic field. Recent work reveals an unexpected magnetization process that cannot be understood within conventional spin-wave or quasiparticle pictures.

I conclude by outlining a theoretical scenario, supported in part by numerical studies, in which increasing magnetization induces an internal gauge flux. This emergent orbital field reorganizes the spinon spectrum into relativistic Landau levels, providing a novel mechanism for field-driven reconstruction in a fractionalized magnet.

The r-process, a series of rapid neutron-capture reactions in cataclysmic astrophysical events such as neutron star mergers, is responsible for the creation of roughly half of the heavy nuclei in our universe. The conditions present in these events are such that the neutron-capture reactions occur on a time scale much shorter than the lifetime of the nuclei involved and the process therefore proceeds through reactions on short-lived neutron-rich nuclei that have mostly never been observed in the laboratory. Sensitivity studies have looked at various scenarios for the r-process conditions and identified regions around neutron numbers 82 and 126 where basic nuclear properties have the largest impact on the distribution of produced nuclei. At ANL, a program centered around the ATLAS facility is aimed at improving access to these nuclei and developing the tools to measure the most critical quantities to constrain r-process scenarios.

Over the last decade, the CAlifornium Rare Ion Breeder (CARIBU) addition to the ATLAS superconducting linac facility provided access to neutron-rich nuclei around the N=82 neutron shell closure that allowed us to gather data that, together with simulations that reverse-engineered the r-process, provided a better understanding of the astrophysical conditions necessary to reproduce the main r-process abundance peak. Additional information is needed to confirm these findings and that requires access to isotopes outside the range of those accessible by current facilities. We have therefore undertaken an upgrade of CARIBU, called nuCARIBU, which makes use of a novel high-intensity-cyclotron based neutron generator irradiating a highly enriched 235U target to increase the fission fragment yield and allow these studies to be extended to even more exotic nuclei in the N=82 region. In addition, the sensitivity studies highlighted another region of high interest, the neutron-rich region “east” of 208Pb, as a particularly sensitive probe for the N=126 abundance peak. This region has proven to be very difficult to access with standard production techniques and ATLAS is building a new facility, the N=126 factory, which uses a different production mechanism to access it. It takes advantage of the unique high-intensity heavy-ion beams at around 10 MeV/u available at ATLAS to produce these nuclei by multi-nucleon transfer reactions and separate them using the techniques developed at CARIBU for fission fragments.

The talk will present the basic nuclear physics inputs required to understand the r-process, together with the existing ATLAS, nuCARIBU and N=126 facilities. The constraints on astrophysical r-process conditions obtained in the CARIBU campaign will also be presented, together with a brief overview of the current research programs at these facilities.

This work is supported by the U.S. Department of Energy, Office of Nuclear Physics, under contract No. DE-AC02-06CH11357, and uses resources from ANL’s ATLAS facility, an Office of Science National User Facility.

TBA

Particle exchange statistics is a fundamental characteristic of quantum matter, conventionally thought to be constrained to either fermionic or bosonic. Each type gives distinct phenomena: fermions and the consequent exclusion principle lead to the structure of the periodic table and properties of metals, while bosons and their bunching give lasers and superfluidity.

I will discuss recent research in our group that has shown other exchange statistics are possible (beyond already-known anyons, which are restricted to two dimensions) and naturally emerge as excitations in spin models. These “paraparticles” admit non-interacting theories, unlike anyons, and I will describe our vision of using this to form the foundation of new analytic and numerical methods to provide a window into correlated matter.

The department will celebrate our students, faculty, and staff at the 2026 Honors Day celebration on May 4.