LNS Special Seminars - 2019



4:00 p.m., Kolker Room, 26-414

Frontiers in Nuclear Astrophysics

Zachary Meisel, Ohio University

When matter is added to one of the densest possible objects in the universe, does that object expand or contract in size? Where were the elements from zinc to tin made? Answers to these seemingly simple questions have remained elusive over a century of nuclear astrophysics research. Recent opportunities, including the dawn of multi-messenger astronomy and the upcoming Facility for Rare Isotope Beams, place us at a unique time to provide solutions. I will discuss ongoing work and future plans at the frontiers of nuclear astrophysics experiment, focusing on new techniques employing radioactive ion beams that will improve constraints on the properties of ultradense matter and the origin of the heavy elements. I will also discuss the interplay between nuclear physics and models of astrophysical phenomena, showing how new approaches to modeling can be used to prioritize experimental efforts. 


4:00 p.m., Kolker Room, 26-414

Revolutionizing High Energy Physics with Plasma Wakefield Acceleration

Spencer J. Gessner, CERN

High energy physics is currently at an impasse. The simplest supersymmetric models are disfavored by recent LHC results and decades of dark matter searches have seen nothing. Linear Colliders like the ILC and CLIC are ready to be built, but the HEP community is divided over funding a single large project at the expense of many others. Is there a technology that can deliver high-energy, high-quality particle beams, while remaining compact, efficient, and inexpensive? In this talk, I will discuss recent advances in beam-driven plasma wakefield acceleration and the critical next steps towards the first HEP applications based on plasma acceleration. 


4:00 p.m., Kolker Room, 26-414

Radio Searches for Neutrinos at the Cosmic and Energy Frontiers

Stephanie Wissel, California Polytechnic State University


Cosmic neutrinos probe fundamental physics at scales far beyond the reach of terrestrial accelerators or other cosmic messenger particles. The low expected flux of cosmic neutrinos drives the need for neutrino experiments to achieve larger exposures and lower thresholds. Radio experiments can achieve such large exposures by taking advantage of the coherent broadband radio emission resulting from ultra-high-energy (E›1017 eV) neutrino interactions. In this talk, I will review results from current radio experiments, like ANITA, and discuss future concepts, like BEACON and RNO/ARA, aimed at understanding cosmic engines and exploring particle interactions at the highest energies.


4:00 p.m., Kolker Room, 26-414

Precision Spectroscopy of “Hot” Atoms and Molecules

Ronald Fernando Garcia Ruiz, CERN


Measurements of atomic and molecular structures allow access to observables that are key to our understanding of the nuclear many-body problem, the study of fundamental symmetries, and the search for new physics. In the atom, for example, hyperfine structure measurements provide fundamental properties of the atomic nucleus: spins, electromagnetic moments, and charge radii. Moreover, a precise knowledge of the interaction between the nucleus and the surrounding electrons can provide constraints on the existence of new particles. On the other hand, molecular systems offer new opportunities to explore the nuclear electroweak structure. In this talk, I will present recent results from laser spectroscopy experiments of exotic atoms and molecules in extreme regions of the nuclear chart, where short-lived nuclei are produced in minuscule quantities (≺ 100 ions/s). The relevance of these results to the recent advances in nuclear theory, and their connection with some of the outstanding questions of nuclear science will be discussed. Future experimental developments that aim to extend the current limits of precision and sensitivity will be illustrated.


3:00 p.m., Kolker Room, 26-414

Black Holes: From Rejection, to Experimental Evidence, to Suprises and Misconceptions

Prof. Bruno Coppi, MIT


The difficult path of the Black Hole concept -- from Princeton where it blossomed originally, to (our) Cambridge -- is reviewed and re-lived. A series of surprises and misconceptions concerning astrophysical objects identified as Black Holes is illustrated, together with the mysteries that remain to be faced.


2:00 p.m., Kolker Room, 26-414

U.S. Nuclear Weapons Modernization

Roy Schwitters, The University of Texas at Austin


The US last detonated a nuclear weapon in 1992 in an underground test in Nevada. By 1994, the Department of Energy’s National Nuclear Security Administration (NNSA) launched its science-based stockpile stewardship program (SSP) designed specifically to ensure the safety, security, and effectiveness of US nuclear weapons without underground nuclear testing. Today, one quarter century later, the scientists and engineers at NNSA’s national laboratories and associated facilities, have succeeded at this task by a thorough modernization of tools, methods, and ideas about stewarding nuclear weapons. Key enablers were development and employment of specific new experimental capabilities, creation of modern, 3D weapon simulation codes, and investment and acquisition in high-end supercomputers, which in turn led to more detailed understanding of relevant physical processes, and enabled extraction of the high value of the US underground test archive. All of this was knitted together by rigorous application of processes to quantify performance margins and uncertainties.

Looking ahead to the next generation of SSP, issues of responsiveness, agility, and efficiency of the nuclear weapons enterprise led the departments of Defense and Energy to seek a stockpile with fewer weapon types, while maintaining current capabilities. The “3+2” strategy envisaged three sets of “interoperable” nuclear components serving both Air Force ICBMs and Navy SLBMs, and two air-delivered weapons. The 2018 Nuclear Posture Review added a different mix of weapons to the near future stockpile and NNSA’s FY2019 plans detail only the first round of interoperable systems.

However, nuclear threats worldwide are quite different today compared to 1992-94, with more players and, potentially, greater threats. What is known is our SSP approach to stockpile stewardship---without nuclear testing---works. To be sure, there will be future technical challenges and opportunities to be faced: high performance computing may experience limits to growth, while new experimental approaches may be coming into focus to address key performance questions definitively in non-explosive nuclear experiments. Continuous improvement---modernization---of SSP will remain crucial to US deterrence in paving the way to deeper understanding and, perhaps someday, control of these threats to humanity.

Technical issues related to these points will be addressed in the talk.

This talk is a joint event hosted with MIT NSE


12:00 p.m., Kolker Room, 26-414

Dark Photon Search with the Beam Dump Experiment DarkMESA

Patrick Achenbach, Mainz University


At the MESA accelerator in Mainz, Germany, the parasitic electron beam dump experiment DarkMESA is under construction. It has a powerful discovery potential for dark sector particles in the light mass range below 100 MeV. Their possible existence is a candidate explanation for the longstanding dark matter problem. DarkMESA will benefit from the beam energy being below pion production threshold, thus producing very little beam-related background, and the very stable and continuous beam conditions necessary for the main parity-violation experiment. The detector will be constructed from homogeneous calorimeters made of high-density Cherenkov radiators surrounded by a veto system. Advantages are their speed and relatively low sensitivity to background neutrons. The first stage will comprise a mass of 4100 kg.