Louise Skinnari
Searching for needles in the haystack at the LHC and beyond
Abstract:
The Large Hadron Collider (LHC) is the world’s most energetic particle accelerator complex, colliding protons at close to the speed of light. The LHC provides an extremely powerful tool to address fundamental questions about our Universe, including the nature of dark matter, the observed matter-antimatter asymmetry, and the origin of the large difference between the electroweak and Planck energy scales. The LHC is scheduled to be upgraded to its high luminosity counterpart (HL-LHC) in a few years. The HL-LHC will significantly increase the intensity of the proton collisions, in turn enabling the LHC experiments to collect immense data sets to measure properties of the Higgs boson is great detail, probe very rare Standard Model processes, and search for signs of new physics beyond the well-established Standard Model. The increase in intensity, although scientifically exciting, comes at the price of extremely challenging experimental data-taking conditions. These are particularly challenging for the real-time data filtering ('trigger') systems that are responsible for deciding which collision events to read out and store for later analysis. In this colloquium, I will discuss the motivation and physics potential of the high luminosity LHC upgrade, as well as some of the associated experimental challenges, in particular in the context of the CMS experiment's trigger system.
Katie Bouman
Seeing Beyond the Blur: Imaging Black Holes with Increasingly Strong Assumptions
Abstract:
At the heart of our Milky Way galaxy lies a supermassive black hole called Sagittarius A* that is evolving on the timescale of mere minutes. This talk will present the methods and procedures used to produce the first images of Sagittarius A* as well as discuss future directions we are taking to leverage machine learning to sharpen our view of the black hole, including mapping its evolving environment in 3D. It has been theorized for decades that a black hole will leave a "shadow" on a background of hot gas. However, due to its small size, traditional imaging approaches require an Earth-sized radio telescope. In this talk, I discuss techniques we have developed to photograph a black hole using the Event Horizon Telescope, a network of telescopes scattered across the globe. Recovering an image from this data requires solving an ill-posed inverse problem which necessitates the use of image priors to reduce the space of possible solutions. Although we have learned a lot from these initial images already, remaining scientific questions motivate us to improve this computational telescope to see black hole phenomena still invisible to us. In particular, we will discuss approaches we have developed to incorporate data-driven diffusion model priors into the imaging process to sharpen our view of the black hole and understand the sensitivity of the image to different underlying assumptions. Additionally, we will discuss how we have developed techniques that allow us to extract the evolving structure of our own Milky Way's black hole over the course of a night. In particular, we introduce Orbital Black Hole Tomography, which integrates known physics with a neural representation to map evolving flaring emission around the black hole in 3D for the first time.
Shu-Heng Shao
Non-invertible symmetries: From Ising Model to Pion Decay
Abstract:
I will discuss recent developments on a novel kind of global symmetry, the non-invertible symmetry. It is implemented by conserved operators that do not have an inverse, going outside the paradigm set by Wigner's theorem. I will start with the example in the Ising lattice model, and then discuss applications in pion decay and axion physics.
hosted by:Philip Harris
Ibles Olcina Samblas
New constraints on WIMP dark matter from the LUX-ZEPLIN (LZ) experiment
Abstract:
Dark matter detection experiments based on liquid xenon time projection chambers have been steadily increasing in sensitivity to the weakly interacting massive particle (WIMP) over the past two decades. The LZ experiment, employing a two-phase xenon time projection chamber containing 7,000 kilograms of liquid xenon, currently leads the way. Recently, the collaboration released new results from a combined analysis using data from the 2022 and 2024 science campaigns, amounting to a live exposure of 4.2 tonne-years. No evidence for an excess over expected backgrounds was found across all the test WIMP masses. The resulting limit on the spin-independent WIMP-nucleon cross section is world-leading for masses above 9 GeV/c2, surpassing previous best limits by about a factor of four. In this talk, I will describe the new results---including a new technique to actively tag background electronic recoils from Pb-214 beta decays, the observation of charge-suppressed two-neutrino double electron capture events from Xe-124 decays, and the bias mitigation technique called "salting"---and discuss what the future plans for the experiment are.
Jamie Rankin
From Interstellar Space to the Sun’s Embrace: Cosmic Ray Journeys through the Heliosphere
Abstract:
Over a century since their discovery, cosmic rays remain a compelling subject of inquiry in the fields of particle and space physics. These fully ionized atomic nuclei – comprised of practically all known elements of the periodic table – trace paths through the galaxy (and in some cases, from beyond) that cover vast spatial distances, and span over 14 decades in energy (~MeV to a few hundred EeV observed so far). Although origins at all scales are still not fully understood, the last decade has led to some especially critical breakthroughs in understanding, particularly related to their transport and acceleration. This talk focuses on key insights primarily gained from space-based observations of cosmic rays, ranging from ~MeV to ~TeV, whose trajectories get modified by the dynamics and presence of our own stellar astrosphere, the “heliosphere”. It will survey the key findings derived from in-situ measurements at various locations throughout the solar system – including those at record-setting distances near and far from the Sun – and venture beyond the cosmic rays themselves to emphasize what they reveal about how the Sun interacts with its surrounding interstellar environment, the size and structure of the heliosphere, and the physics of particle-plasma interactions applicable to many solar and astrophysical phenomena.
