BNL Physics Department Videos

Physics Colloquium of 27 July 2022
"Probing antimatter gravity with trapped antihydrogen"
Chris Rasmussen, CERN

Einstein's Weak Equivalence Principle (WEP) demands that all objects fall with the same acceleration regardless of their composition, and this has been experimentally verified to extraordinary precision in ordinary matter. For antimatter objects though, a direct experimental test has yet to be achieved. ALPHA-g is a new experiment aiming to measure the gravitational mass of antimatter through the careful release of magnetically trapped antihydrogen atoms. In this colloquium, I will give an overview of how an antimatter gravity measurement will be achieved in ALPHA-g, and outline the developments that have enabled us to attempt such a measurement.

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Physics Colloquium of 10 May 2022
"Fast radio burst science results from CHIME"
Kendrick Smith, Perimeter Institute for Theoretical Physics

Fast radio bursts (FRB's) are a recently discovered, poorly understood class of transient event, and understanding their origin has become a central problem in astrophysics. I will present FRB science results from CHIME, a new interferometric telescope at radio frequencies 400-800 MHz. In the ~3 years since first light, CHIME has found ~20 times more FRB's than all other telescopes combined, including ~60 new repeating FRB's, the first repeating FRB with periodic activity, a giant pulse from a Galactic magnetar which may be an FRB in our own galaxy, and millisecond periodicity in FRB sub-pulses. These results were made possible by new algorithms which can be used to build radio telescopes orders of magnitude more powerful than CHIME. I will briefly describe two upcoming projects: outrigger telescopes for CHIME (starting 2022) and CHORD, a new telescope with ~10 times the CHIME mapping speed (starting 2024).

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Physics Colloquium of 3 May 2022
"Soft Pions and The Dynamics of the Chiral Phase Transition in QCD"
Derek Teaney, SBU

I will first review lattice simulations of the QCD phase diagram, focusing on chiral symmetry and chiral symmetry breaking. In the limit of two massless quark flavors (up and down) the chiral phase transition is second order and is in the O(4) universality class. The fingerprints of this critical point are seen in lattice simulations of real world QCD. Next I will review heavy ion experiments, presenting an overview of some of the most important measurements from heavy ion collisions. These measurements provide compelling evidence that classical hydrodynamics is an appropriate effective theory for understanding these collisions. In current hydrodynamic simulations of these events, chiral symmetry breaking and its consequences are largely ignored. However, if the quark mass is small enough, one would expect that the pattern of chiral symmetry breaking seen on the lattice could provide a useful organizing principle for hydrodynamics, increasing its predictive power. I describe our efforts to simulate the real time dynamics of the O(4) critical point using hydrodynamics. Then I point out some discrepancies between the measured yields of soft pions and current hydrodynamic simulations. I suggest that incorporating the chiral phase transition into the hydrodynamic description could fix the discrepancies.

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Physics Colloquium of 26 April 2022
"Dark Sectors and Their Observability"
Kathryn Zurek, Caltech

The nature of the dark matter remains one of the most compelling outstanding questions in physics. Theoretical and experimental focus has been directed in the last several decades on New Physics at the weak scale, where the dark matter dynamics are parasitic on the ordinary standard model forces. We are now looking beyond the weak scale dark matter paradigm towards theories of dark matter with their own dark sector forces. These theories lead to many new signatures both in the cosmos and in the laboratory, and ideas to search for these hidden sectors abound. I describe some of these new ideas, focusing on quantum materials and quantum sensors.

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Physics Colloquium of 19 April 2022
"Assessing Gender Bias in Particle Physics and Social Science Recommendations for Academic Jobs"
Robert Bernstein, Fermilab

We investigated [1] gender bias in letters of recommendation as a possible cause of the under-representation of women in Experimental Particle Physics (EPP), where about 15% of faculty are female—well below the 60% level in psychology and sociology. We analyzed 2206 letters in EPP and these two social sciences using standard lexical measures as well as two new measures: author status and an open-ended search for gendered language. In contrast to former studies, women were not depicted as more communal, less agentic, or less standout. Lexical measures revealed few gender differences in either discipline. The open-ended analysis revealed disparities favoring women in social science and men in EPP. However, female EPP candidates were characterized as "brilliant" in nearly three times as many letters as were men.

References: [1]

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Physics Colloquium of 29 March 2022
"Exploring the Mysteries of QCD with Transverse Momenta"
Iain Stewart, MIT

Quantum Chromodynamics (QCD), the theory of the strong interaction, is a remarkable quantum field theory, giving rise to interesting emergent phenomena. For many of these we are still seeking to unravel their precise nature, including confinement - whereby quarks and gluons are trapped inside relativistic bound states like the proton - and hadronization - whereby energetic quarks and gluons produced in a high energy collision evolve into bound pions and other hadrons. In this talk I discuss new insights into QCD obtained from the study of transverse momentum dependence, including the distributions of confined and hadronizing particles, final state interactions, and spin-momentum correlations. This multi-faceted program relies on foundational results in continuum field theory, lattice QCD calculations, experimental measurements, and phenomenological analyses. The bright future of this field will be particularly influenced by the upcoming electron ion collider at BNL.

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Physics Colloquium of 8 March 2022
"From the Kondo Problem to Wilson Lines —- Defects in Many-Body Systems"
Zohar Komargodski, Simons Center for Geometry and Physics, Stony Brook Univ.

We review the role of defects in many-body systems and in Quantum Field Theory. The Kondo defect has led to the Renormalization-Group and Wilson line defects have been paramount in the classification of low-energy phases of gauge theories. We review some recent progress on the topic of defects in magnets and in gauge theories. We define a notion of zero-temperature impurity entropy and argue that it captures the number of degrees of freedom on the impurity. We demonstrate this idea for magnetic impurities, pinning field impurities, and Wilson lines, making several experimental predictions on the way.

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Physics Colloquium of 1 March 2022
"Exploring the Flavor Structure of Nucleon Sea with Lepton-Pair Production"
Jen-Chieh Peng, University of Illinois at Urbana-Champaign

Direct experimental evidence for point-like constituents in the nucleons was first found in the electron deep inelastic scattering (DIS) experiment. The discovery of the valence and sea quark structures in the nucleons inspired the formulation of Quantum Chromodynamics (QCD) as the gauge field theory governing the strong interaction. A surprisingly large asymmetry between the up and down sea quark distributions in the nucleon was observed in DIS and the lepton-pair production experiments. In this talk, I discuss the current status of our knowledge on the flavor structure of the nucleon sea. I will also discuss the progress in identifying the "intrinsic" sea components in the nucleons. Recent results from the Fermilab SeaQuest experiment to extend the measurement of sea-quark flavor structure to large-x region will be presented. Prospect for future studies on nucleon sea will also be discussed.

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Other Listings

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