Physikalisches Kolloquium

Programm für das Sommersemester 2021

Tuesdays, 16 Uhr c.t.

Institut für Kernphysik, Remote Seminar
live at Zoom

13.04.21Hartmut Wittig und Martin Fertl, University of Mainz
The long-persisting discrepancy between the Standard Model prediction of the anomalous magnetic moment of the muon (aµ) and its latest measurement provides an intriguing hint to new physics. Since 2017, the Muon g − 2 Theory Initiative has assessed the theoretical prediction for aµ, focusing on the contributions from the strong interaction, which account for the dominant part of the uncertainty. The latest estimate for the Standard Model prediction, which was published in a recent White Paper, has failed to resolve the discrepancy with the experimental measurement at Brookhaven National Laboratory, which stands at 3.7 standard deviations. At Fermi National Accelerator Laboratory, USA, the Muon g-2 collaboration is performing a new measurement of aµ aiming at an ultimately fourfold smaller uncertainty than achieved with the predecessor experiment. To extract the value of aµ a clock comparison experiment is performed with spin-polarized muons confined in a superbly controlled electric and magnetic field environment. The deviation of the Larmor from the cyclotron frequency, the anomalous spin precession frequency, is determined while a high-precision measurement of the magnetic field environment is performed using nuclear magnetic resonance techniques. We will provide an introduction to the current theory prediction before we will present and discuss the first results of the FNAL experiment from its 2018 science run.
16:15 Uhr s.t., at Recording of the presentation

20.04.21Mehran Kardar, Massachusetts Institute of Technology, Cambridge, USA
Affinity maturation (AM) is the process through which the immune system evolves antibodies (Abs) which efficiently bind to antigens (Ags), e.g. to spikes on the surface of a virus. This process involves competition between B-cells: those that ingest more Ags receive signals (from T helper cells) to replicate and mutate for another round of competition. Modeling this process, we find that the affinity of the resulting Abs is a non-monotonic function of the target (e.g. viral spike) density, with the strongest binding at an intermediate density (set by the two-arm structure of the antibody). We argue that, to evade the immune system, most viruses evolve high spike densities (SDs). An exception is HIV whose SD is two orders of magnitude lower than other viruses. However, HIV also interferes with AM by depleting T helper cells, a key component of Ab evolution. We find that T helper cell depletion results in high affinity antibodies when SD is high, but not if SD is low. This special feature of HIV infection may have led to the evolution of a low SD to avoid potent immune responses early on in infection. Our modeling also provides guides for design of vaccination strategies against rapidly mutating viruses.
16:15 Uhr s.t., at Recording of the presentation

27.04.21Jason Detwiler, University of Washington, USA
Neutrinos are known for their elusive nature due to their extremely small cross section for scattering off of individual nucleons inside of nuclei. However they can also undergo billiard-ball-like coherent elastic scattering off of entire nuclei, with a greatly enhanced cross section. This coherent elastic neutrino-nucleus scattering (CEvNS) is an important process in core-collapse supernovae, and can also be used for astrophysical and terrestrial neutrino detection. The coherence of the interaction can also amplify potential non-standard interactions between neutrinos and quarks, making it an ideal mode for testing as-yet unprobed physics beyond the Standard Model. Although CEvNS was predicted in 1974, its first observation was only recently made in 2017 by the COHERENT collaboration, leveraging decades of Dark Matter detector R&D that has yielded technologies with sufficient sensitivity to observe the ultra-faint nuclear recoils that are the only signatures of the interaction's occurrence. COHERENT's discovery was also enabled by its nearly ideal pulsed source of pion-decay neutrinos: the beam dump of the Spallation Neutron Source at Oak Ridge National Laboratory. In this talk, I will discuss the physics of CEvNS and its challenging measurement. I'll describe COHERENT's first observation of CEvNS using the world's first hand-held neutrino detector, a CsI scintillating crystal. I will then detail our more recent first observation of CEvNS with argon using a scintillating volume of liquid Ar, including our updated sensitivity to non-standard neutrino interactions and other physics. I'll also describe our plans to field two more detectors using NaI scintillating crystals as well as an array of germanium radiation detectors, and our longer term plans to build multiple ton-scale experiments at a new beam stop with significantly improved sensitivity.
16:15 Uhr s.t., at Slides

04.05.21Gia Dvali, Max Plank Institute of Physics, Munich
Understanding the origin of hierarchies is one of the main driving forces of today's fundamental research. The well-known examples are provided by the hierarchy between the weak and Planck scales, the hierarchy between neutrino and electron masses and the hierarchy between the Planck scale and the vacuum energy of the present Universe. Sometimes these puzzles are classified as so-called ``naturalness problems". Historically, in the case of proton/pion mass hierarchy, such questions led to advances that changed modern particle physics. In this talk we review certain representative examples when the hierarchy can be taken as a serious indication for new physics. We also review cases when a seeming naturalness problem is nullified by consistency of the theory. We give an example of the celebrated naturalness puzzle of the cosmological term. This however turns out to be fictitious, since the consistency of the S-matrix formulation demands that the cosmological constant is excluded from the energy budget of our Universe.
16:15 Uhr s.t., at Recording of the presentation

11.05.21Achim Stahl, RWTH Aachen, Germany
Gravitational waves opened a new window into the universe. The current generation of gravitational wave detectors demonstrated the existence of gravitational waves and made a number of highly interesting discoveries. In parallel with their operation we are developing a new generation of telescopes with a sensitivity goes beyond the final sensitivity of the current telescopes by at least an order of magnitude. The Einstein Telescope will be the European project of the new generation. After an introduction of gravitational waves and a few highlights from the current observation runs, I will discuss the perspectives and technologies necessary to improve their performance. I will introduce the Einstein Telescope and present a few example of the science we might expect
16:15 Uhr s.t., at Recording of the presentation

18.05.21Kathrin Valerius, Karlsruher Institute of Technology, Germany
News on the Neutrino-Mass Measurement
16:15 Uhr s.t., at Recording of the presentation

01.06.21Katia Parodi, University of Munich, Germany
High Precision Ion Therapy
16:15 Uhr s.t., at Attachement

08.06.21Jens Erler, University of Mainz
Half a century ago the foundations underpinning the gauge theories of the strong, weak and electromagnetic interactions had been laid out, and the age of precision calculations for its tests and the determination of its parameters could begin. We recall some of the history with an emphasis on the role played by electroweak precision tests. While in the past theoretical ideas have often preceded experimental discoveries, the years and decades ahead of us are in desperate need of experimental guidance.
16:15 Uhr s.t., at Zoom

15.06.21Helmut Satz, University of Bielefeld, Germany
In recent years, the study of swarm formation and structure has become a challenging field of research in which biology and physics overlap. It was shown that mathematical models of many identical components subject to simple interactions produce behavior patterns similar to those of swarms, as observed in high statistics measurments of starling flocks in Rome by the EU Starflag collaboration. Swarm behavior thus is an instance of selforganisation - there is no leader or formation plan.
16:15 Uhr s.t., at Recording of the presentation

22.06.21Horst Geckeis, Karlsruher Institute of Technology, Germany
Endlagerstätten in Deutschland
16:15 Uhr s.t., at Recording of the presentation

29.06.21Norbert M. Linke, Joint Quantum Institute and Department of Physics, University of Maryland, College Park, MD 20742, USA
Trapped ions give us a high degree of detailed control of their various quantum degrees of freedom, which has enabled a large number of experiments in quantum optics, quantum computing, simulation and networking as well as precision metrology and others. We present a quantum architecture consisting of a linear chain of trapped 171 Yb+ ions with individual laser beam addressing and readout. The collective modes of motion in the chain are used to efficiently produce entangling gates between any qubit pair. In combination with a classical software stack, this becomes in effect an arbitrarily programmable fully connected quantum computer. Over the past five years, we have employed this experiment to demonstrate a variety of quantum algorithms with the help of a community of academic partners, including cross-hardware comparisons with commercially developed systems and digital quantum simulations of models from high-energy physics and other areas. We also use the same level of control to study interesting quantum phenomena using the motional degrees of freedom directly, such as exotic para particles and Hubbard models of phonons. This talk will give recent highlights from both of these approaches and discuss improvements in trap technology for scaling up as well as other ideas for the future.
16:15 Uhr s.t., at Recording of the presentation

06.07.21Ken Carslaw, University of Leeds, Great Britain
Clouds containing a mixture of ice and supercooled water are expected to become more reflective in a warmer world as the ice is increasingly replaced by water. This response causes a negative “cloud-phase” climate feedback that acts to dampen global warming. In this presentation I will show that quantification of this cloud response hinges on understanding the properties of the rare particles that initiate ice formation – ice-nucleating particles. I will show results from modelling and observations that demonstrate the importance of these particles for cloud reflectivity. Substantial recent developments in our understanding of ice-nucleating particles from laboratory and field measurements now enable us to build reasonable global models of their distribution and to determine which properties matter for climate change.
16:15 Uhr s.t., at Zoom

13.07.21Nick Hutzler, Caltech, California Institute of Technology, USA
The fact that the universe is made entirely out of matter, and contains no free anti-matter, has no physical explanation. The unknown process that created matter in the universe must violate a number of fundamental symmetries, including those that forbid the existence of certain electromagnetic moments of fundamental particles whose signatures are amplified by the large internal fields in polar molecules. We discuss spectroscopic and theoretical investigations into polyatomic molecules that uniquely combine multiple desirable features for precision measurement, such as high polarizability through symmetry-lowering mechanical motions, novel electronic and bonding structures, laser cooling, and exotic nuclei.
16:15 Uhr s.t., at Zoom

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Prof. Dr. Matthias Schott
Institut für Physik, ETAP

Prof. Dr. Frank Maas
Institut für Kernphysik