Theory Center

SFB Colloquium

Past Seminars

04. 05. 2023 at 14:00 S2 11/10	SFB Colloquium Gaute Hagen (ORNL) Frontiers in ab-initio computations of atomic nuclei High performance computing, many-body methods with polynomial scaling, and ideas from effective-field-theory is pushing the frontier of ab-initio computations of nuclei. Here I report on advances in coupled-cluster computations of nuclei starting from chiral Hamiltonians. The ab-initio approach can now be used to address fundamental questions related to the nature of the neutrino by accurate computations of neutrino-less double beta decay and making first steps towards neutrino-nucleus scattering on relevant nuclei. Global surveys of bulk properties of medium-mass and neutron- rich nuclei from ab-initio approaches are possible by using reference states that break rotational symmetry. These calculations have revealed systematic trends of charge radii in various isotopic chains, questioned the existence of certain magic shell closures in neutron-rich nuclei, and confrontation with data have exposed challenges for ab- initio theory. By restoring rotational symmetry, we have made predictions for the rotational structure of neutron-rich neon and magnesium isotopes. In addition to entire regions of the nuclear chart now being targeted by ab-initio computations, entirely new ways to make quantified predictions are becoming possible by the development of accurate emulators of ab-initio calculations. These emulators reduce the computational cost by many orders of magnitude. This allows us to perform global sensitivity analysis, and use novel statistical tools in making quantified predictions of nuclei. Recently we used these tools to predict the neutron skin in 208Pb, and found that the neutron-skin is smaller and more precise than a recent extraction from parity-violating electron scattering. We have also addressed the question of what drives deformation in exotic neon and magnesium isotopes from chiral interactions.
19. 12. 2022 at 14:00 S2 11/10	SFB Colloquium Bernhard Maass (Argonne National Laboratory) First results from ATLANTIS: Collinear Laser Spectroscopy at Argonne National Laboratory In recent years, a laser spectroscopy beamline was installed and commissioned at the ATLAS facility at Argonne National Laboratory. Experiments using this new setup were conducted on fission fragments from the CARIBU Californium source. This overview will provide details on the measurements performed, initial results, and a look ahead to future laser spectroscopy experiments at ANL.
21. 07. 2022 at 14:00 S2 11/10 (plus zoom)	SFB Colloquium Fernando Montes (NSCL) Rare isotopes and the origin of the not so heavy elements Stellar explosions and colliding neutron stars are important sources of the chemical elements in nature. While some of the astrophysical processes responsible for element creation are well understood, others have remained elusive for decades. Processes creating elements often involve short lived radioactive isotopes that can be produced at accelerator facilities. Studies with these isotopes allow us to constrain the relevant nuclear reaction rates so one can understand in the laboratory how elements are created. In this talk, I will focus on the lighter heavy elements of the first r-process peak, between strontium and silver, and will review the important role that nuclear reactions play in understanding stellar explosions. I will discuss recent endeavors to experimentally constraint some of the relevant nuclear reaction rates and will emphasize the role of the newly commissioned SECAR (SEparator for CApture Reactions) recoil separator at the Facility for Rare Isotope Beams (FRIB) as well as new initiatives, and plans for the future.
30. 06. 2022 at 14:00 S2 14 / 24 (plus zoom)	SFB Colloquium Iris Dillmann (TRIUMF) The TRISR Project - A Storage Ring for Neutron Captures on Radioactive Nuclei Heavy-ion storage rings connected to radioactive beam facilities offer a unique environment for nuclear physics experiments. However, so far they have been only coupled to in-flight fragmentation facilities, for example the ESR and the CRYRING at GSI Darmstadt/ Germany, the CSR at HIRF in Lanzhou/ China, and the Rare RI Ring at RIKEN Nishina Center in Japan. Neutron capture reactions play a crucial role for the understanding of the synthesis of elements heavier than iron in stars and stellar explosions via the slow (s), intermediate (i), and rapid (r) neutron capture processes. Whereas most of the s-process neutron captures occur on stable or long-lived nuclei along the line of stability and have been experimentally constrained in the past decades, measuring directly the neutron capture cross sections of short-lived nuclides (T1/2 << 1 y) has been so far out of reach and lead to large deviations between various Hauser-Feshbach predictions for very neutron-rich nuclei. Recently, a new method to couple a neutron-producing "facility" to a RIB storage ring was outlined [1]. The initial proposal involved a storage ring running through a high flux fission reactor to achieve high enough neutron densities. Later, a facility with a spallation neutron source was suggested [2], a proposal that is presently investigated at Los Alamos National Laboratory [3]. Our storage ring project at TRIUMF proposes to use instead a compact neutron generator coupled to a low-energy storage ring (E= 0.1-10 MeV/u) and the existing ISAC radioactive beam facility. The project is currently seeking funding in Canada for a feasibility study. The TRISR project is presented, and measurements are outlined that would become possible, especially with the availability of clean, intense radioisotope beams from the new ARIEL facility. If this world-wide unique facility is funded and built, it could become a key player and lead within a decade of operation to a major reduction of uncertainties for neutron capture cross sections of radioactive nuclei. [1] R. Reifarth and Y. Litvinov, Phys. Rev. ST Accel. Beams 17 (2014) 014701. [2] R. Reifarth et al., Phys. Rev. Accel. Beams 20 (2017) 044701. [3] S. Mosby et al., Los Alamos National Laboratory preprint LA-UR-21-30261 (2021).
19. 05. 2022 at 14:00 S2 11/10 (plus zoom)	SFB Colloquium Pieter Doornenbal (RIKEN) Latest results and future potential for in-beam gamma-ray spectroscopy at the RIBF Since its first beam in 2006, the Radioactive Isotope Beam Factory (RIBF) of the RIKEN Nishina Center provides the world's most intense secondary beams at intermediate energies. Its capabilities have been demonstrated by the discovery of almost 200 new isotopes, and future intensity upgrades are planned in order to maintain its leading role. In-beam gamma-ray spectroscopy is a powerful approach to study properties of the most exotic nuclei with the secondary beams provided at the RIBF. A large physics program makes use of this tool to address various aspects of nuclear structure. The presentation will highlight recent results and key achievements obtained at the RIBF from in-beam gamma-ray spectroscopy, and dare a peek into the facility's future potential.
09. 03. 2022 at 10:30 zoom	SFB Colloquium Liss Rodriguez (CERN) Recent results of collinear laser spectroscopy in 'magic' nuclei: from tin to lead High-resolution collinear laser spectroscopy has been recently performed on a long sequence of tin (Z=50) and lead (Z = 82) isotopes at COLLAPS/CERN. Hyperfine structures and isotope shifts have been measured and high-precision values of electromagnetic moments and charge radii of ground and isomeric states are extracted. Similar quadratic trends are observed for the quadrupole moments of the 11/2- and 13/2+ isomeric states in the semi-magic nuclei. The picture is not the same for the ground states where the pattern changes from linear, in tin, to quadratic, in lead. Differences in charge radii between the high-spin isomeric states and the nuclear ground states, on the other hand, also show a surprisingly similar behaviour. These regularities will be discussed in the framework of nuclear structure with emphasis on how, under certain conditions, simplicity arises out of complexity.
13. 01. 2022 at 14:00 zoom	SFB Colloquium Heiko Hergert (MSU) A New Generation of Many-Body Methods for Nuclear Structure Nowadays, computationally efficient many-body methods can be used to perform first-principles calculations for atomic nuclei up to mass A~150. This progress has made it possible to confront modern two- and three-nucleon interactions from Chiral Effective Field Theory with a wealth of experimental data, and provide important guidance in their ongoing refinement. In my talk, I will focus one such many-body approach, the In-Medium Similarity Renormalization Group (IMSRG). The IMSRG not only offers a means to directly compute certain nuclear properties but also provides a powerful framework for designing "hybrid" methods that allow us to tackle nuclei with strong collective correlations, e.g., due to intrinsic deformation. I will present applications of such IMSRG-based approaches to the first-principles description of (doubly) open-shell nuclei, including candidate nuclei for fundamental symmetry tests. I will also give an overview of new developments that promise to once again increase the capabilities of the IMSRG and related nuclear structure methods in the coming years.
24. 06. 2021 at 14:00 zoom	SFB Colloquium Thomas Papenbrock (University of Tennessee) Effective theories, coupled clusters, and computers: predicting properties of atomic nuclei Recent years have witnessed a sea change in our description of atomic nuclei. Ideas from effective field theory and the renormalization group combined with efficient computational tools, emulators, and accelerators have propelled nuclear theory. Increasingly heavy nuclei are now described using controlled approximations. Machine learning tools and emulators allow us to explore a continuum of interactions at once. This talk highlights some of the recent advances.
17. 06. 2021 at 14:00 zoom	SFB Colloquium Javier Menendez (University of Barcelona) Nuclear neutrinoless double-beta decay: new ideas for improved matrix elements Atomic nuclei could neutrinoless double-beta (0nbb) decay by emitting two electrons, reaching a final nucleus with two more protons and two fewer neutrons than the initial one. Such process, therefore, creates two matter particles (electrons), violating the lepton number conservation of the Standard Model, which is possible if neutrinos are their own antiparticles. 0nbb decay has not been observed so far, but due to its unique potential to shed light on physics beyond the Standard Model, several collaborations worldwide are actively pursuing its detection. The interpretation of 0nbb experiments, however, depends on the nuclear matrix elements (NME) that govern the 0nbb decay rate, but these are poorly known. This theoretical uncertainty limits severely the exploitation of 0nbb experiments. I will present two ways to overcome this limitation and improve our understanding of 0nbb nuclear matrix elements. First, I will show the potential to learn about 0nbb by measuring double Gamow-Teller transitions in double charge-exchange reactions, or electromagnetic double-gamma decays. Second, I will discuss the contribution of a previously neglected short-range nuclear matrix element that can impact significantly the 0nbb decay rate.
03. 12. 2020 at 14:00 zoom	SFB Colloquium Constanca Providencia (University of Coimbra) The interplay between neutron stars and the equation of state I will refer to some results on the implication of neutron star observations on the equation of state, and of the equation of state calibrated to experiments on neutron star properties. The following topics will be discussed: the possible hyperon content and implication on neutron star properties, the formation of light clusters in warm matter, constraining the EoS from the tidal deformability and hybrid stars with large quark cores.
26. 11. 2020 at 14:00 zoom	SFB Colloquium Camilla Hansen (Max Planck Institute for Astronomy, Heidelberg) Linking direct and indirect stellar observation to nuclear reactions Observations of cool, low-mass stars provide the best cosmic traces of current and past nuclear reactions taking place in some of the most extreme environments in the Universe. Spectra of old, low-mass stars provide a multi-dimensional channel in time and space to study the nature, ejecta and nuclear reactions that took place billions of years ago in the first stars. The first stars were massive and exploded as supernovae long ago, however, their chemical finger prints survive in the low-mass stars we can still observe today. Through high-resolution, spectroscopic observations of these old generations of stars, we unveil the physical and chemical properties of the first stars and map the gradual chemical enrichment of the Milky Way. Focussing on the heavy elements, stellar abundances indicate that several formation channels must contribute to their production. Distinct contributions from at least two nuclear processes can be traced indirectly; a slow neutron-capture process associated with asymptotic giant branch stars and a rapid neutron-capture process which is harder to map. Past studies suggested supernovae as formation sites, while recent discoveries challenged this simplistic view. The combination of recent gravitational-wave detections and infrared imaging showed that merger events can create r-process material. However, the spectra provided the first direct detections of newly synthesised r-process material in a neutron star merger. In this talk, I will describe how we observationally can trace the origin of r-process elements in the universe and infer the nature of the first stars despite the fact that these are long gone.
16. 12. 2019 at 14:00 S2 11/10	SFB Colloquium Bernhard Mueller (MPI Garching) Simulations of Core-Collapse Supernovae: Understanding the birth properties of compact objects and beyond Core-collapse supernovae, the explosions of massive stars, have remained one of the outstanding challenges in computational astrophysics for decades, and the mechanism by which they explode has long eluded us. However, there is now a growing number of 3D simulations that develop successful explosions driven by neutrino heating in conjunction with violent aspherical fluid motions. One of the main challenges is now to corroborate the simulations by confronting them with observables. Among these observables, the birth properties of compact remnant are within close reach. Recent 3D models already obtain neutron star masses, kicks, birth spin periods within the observed range, and predict interesting and possible testable correlations between these neutron star properties. Furthermore, 3D simulations of partially successful fallback supernovae suggest a pathway for the formation of black holes with substantial kicks, for which there is increasing observational evidence. I will conclude with an outlook on other observables that may help to further unravel the inner workings of the multi-dimensional neutrino-driven engine.
28. 11. 2019 at 15:15 S2 11/10	SFB Colloquium Valentin Nesterenko (Dubna) Vortical excitations in nucei Intrinsic vortical excitations represent a remarkable kind of the nuclear flow which does not contribute to the continuity equation. Despite an impressive effort in the theory and experiment, vortical modes still have many open problems and their direct experimental observation is yet questionable. In the present talk, we discuss the nuclear vorticity for the remarkable example of the isoscalar E1 toroidal mode. This mode is known in hydrodynamics as a Hill's vortex. In nuclei, it is mainly realized as an isoscalar giant toroidal dipole resonance (TDR). We sketch some TDR features (interplay of TDR and pygmy E1 resonance, deformation impact, etc) predicted by self-consistent microscopic models and outline the experimental status of the TDR. As a new route in exploration of the vortical toroidal flow, we propose to consider individual low-energy toroidal states in light nuclei like 24Mg, 20Ne, 16O,12C, 10Be. The Skyrme QRPA results are compared with AMD+GCM cluster results of Kyoto group. A possible way to identify the toroidal flow in the (e,e') reaction through the interplay of convection and magnetization contributions to transversal form factors is discussed. Besides, we inspect the interplay of E1 toroidal and M2 twist vortical modes.
18. 11. 2019 at 10:00 S2 11/10	SFB Colloquium Alexander Bartl (TNG Technology Consulting) Software Engineering Best Practices Modern software engineering relies on a lot of tools and techniques that aim to make the code easier to write, easier to understand and more maintainable. Automated testing and continuous integration reduce the need to manually check intermediate results again and again while increasing ones trust in ones results. Version control systems like Git not only facilitate collaboration on code, but make it easier to track down bugs. Structuring code to be more readable and having other people actually read it has value even for code that is not meant to be shared but you will have to get back to after months or years when that paper is in its third round of reviews or you're finally writing up your thesis. Integrated development environments (IDEs) may seem much clunkier than simple text editors, but their code analysis makes them powerful. While I had heard about a number of these topics back in academia, most of them were not common practice and I didn't really see their value for the code I wrote as a PhD student. Having seen them in action now, I wish I had used them already back at university. A lot of my colleagues share the sentiment. Hence this talk, in which I will give an introduction to these topics and explain how they can help you with your scientific coding.
20. 08. 2019 at 14:00 S2 11/207	SFB Colloquium Lucas Platter (University of Tennessee) Electroweak processes in effective field theory Electroweak processes provide a unique way of testing nuclear models and the description of the coupling of external currents to nuclei. I will discuss recent progress in the calculation of electroweak processes in the few-body sector. In particular, electroweak capture reactions that also involve the Coulomb interaction are hard to measure experimentally since the cross section is exponentially suppressed due to the Coulomb repulsion. Specifically, I will focus on proton-proton fusion the initial reaction that starts the proton-proton chain reaction network that is generating energy in the sun. I will also address how this reaction is related to muon capture on the deuteron, an experimentally measurable process. For both of these processes, I will also illustrate different methods to quantify the uncertainties of our predictions. If time permits, I will also discuss our recent progress in calculate the decay rate for beta-delayed proton decay of Beryllium-11.
25. 07. 2019 at 14:00 S2 11/10	SFB Colloquium Atsushi Tamii (Research Center for Nuclear Physics, Osaka University, (RCNP-E498 collaboration)) Gamma decay of isovector giant dipole resonances: damping mechanism and fine structure The isovector giant dipole resonances (IVGDR) are described as collective dipole oscillation between neutrons and protons. They commonly exist in any atomic nuclei. The IVGDR is. Gross properties like excitation energy and strength are well reproduced by microscopic models but their width is not yet fully explained owing to the complex damping mechanism. Also pronounced fine structures are observed in heavy nuclei. The present research is focusing on the width and damping mechanism of the IVGDR. We have measured gamma decay from the IVGDR in 90Zr by employing the high-resolution magnetic spectrometer Grand Raiden at RCNP, Osaka University. The target nucleus was excited by proton scattering at 392 MeV. The gamma rays from the IVGDR were detected by eight large-volume LaBr3 detectors developed in Milano. The gamma decay of IVGDR to the ground states was successfully observed in spite of its small branching ratio of 1-2%. I will report on the preliminary results and discuss physical interpretations.
13. 06. 2019 at 14:00 S2 11/10	SFB Colloquium Carlos Bertulani (Texas A&M University-Commerce) Pygmy resonances, neutron skins, and neutron stars In this talk, I will discuss the limitations of nuclear physics in determining the necessary conditions for the description of neutron star masses, radii, and other properties. Some of the latest theoretical and experimental efforts will be reported, with emphasis on the symmetry energy and equation of state of nuclear matter. Perspectives will be discussed of how the ingredients of these physical quantities can be inferred from experiment plus theory.
23. 05. 2019 at 14:00 S2 11/10	SFB Colloquium Ann-Cecilie Larsen (University of Oslo) Constraining neutron capture rates relevant to r-process and i-process nucleosynthesis The element distribution we observe in the Universe, and in particular the diverse abundances of atomic nuclei, tells a fascinating story of nucleosynthesis events that have taken place throughout the 13.7-billion-year-long history starting with the Big Bang. Since the groundbreaking works of Burbidge, Burbidge, Fowler and Hoyle and Cameron in 1957, it has been known that radiative neutron-capture reactions play a major role in synthesizing elements heavier than iron. However, many questions remain when it comes to our understanding of neutron-capture processes in various stellar environments. In particular, the intermediate and rapid neutron-capture processes are very challenging to describe, as they involve neutron-rich nuclei for which there exist little or no data on the much-needed neutron-capture rates. In this contribution, possibilities to obtain indirect, experimental constraints of these rates by means of the Oslo method and the beta-Oslo method will be discussed.
23. 04. 2019 at 14:00 S2 11/10	SFB Colloquium Evan O'Connor (Stockholm University) Core-Collapse Supernovae from 1D to 3D Core-Collapse supernovae are triggered by the implosion and subsequent explosion of the iron core in an evolved massive star. Since the core is shrouded from us by the overlying layers of the star, numerical simulations (and the odd neutrino detection of a Galactic supernova) are our best look into this extreme engine that powers one of the most energetic events in the Universe. Nature is 3D, and it is critical to simulate core-collapse supernovae in three dimensions because of the important hydrodynamic instabilities that can be present, however they are computationally expensive. With 1D and 2D models, we are now able to perform parameterized and systematic studies across a range of stars. Furthermore, in spherical symmetry we are able to achieve excellent agreement between otherwise completely independent codes. In this talk I will present a global comparison in 1D between six core collapse codes, an exploration of parameterized 1D explosions with over 1000 simulations and the beginnings of a systematic study of core collapse in 2D and simulations where we explore fundamentally 3D phenomena. I'll also present new results on the equation of state dependence of black hole formation.
07. 02. 2019 at 14:00 S103/221	SFB Colloquium Michael Wiescher (University of Notre Dame) Nucleosynthesis of Primordial Star Primordial Stars are first generation stars that formed about 400 Million years after the Big Bang. Model simulations predict a mass distribution ranging from ten to several thousand solar masses. Their lifetime is short and a direct observation is unlikely. The observational evidence is in the abundance distribution of the subsequent second/third star generation, which is characterized by large carbon, oxygen abundances, with some more spurious heavier contaminants. This talk will present the various nucleosynthesis patterns possible in a primordial star environment and will discuss present experimental efforts to obtain a better understanding of the associated nuclear reaction rates. Preliminary results have been used to perform first star nucleosynthesis simulations for identifying the main reaction path towards the early origin of carbon and oxygen in our universe.
10. 01. 2019 at 14:00 S2 11/10	SFB Colloquium Wolfram Weise (TU Muenchen) Dense baryonic matter and strangeness in neutron stars This seminar presents a survey of our current understanding of dense baryonic matter from the point of view of hadronic chiral field theories and non-perturbative extensions using functional renormalization group methods. Constraints from neutron star observations are briefly reviewed. The so-called 'hyperon puzzle' in neutron star matter is outlined and a possible solution of this puzzle is discussed on the basis of hyperon-nuclear two- and three-body forces derived from chiral SU(3) effective field theory.
13. 12. 2018 at 14:00 S2 11/10	SFB Colloquium Daniel Phillips (Ohio University) Knowing What You Don't Know: Nuclear Physics, Effective Field Theory, and Uncertainty Quantification For almost a century physicists have devoted intense attention to teasing out the nature of the nuclear force. But there remains much that we do not know about the way neutrons and protons interact, and the way that they come together to form nuclei. In this talk, I will show how two tools, effective field theory and Bayesian probability theory, can provide quantitative assessments of the impact of the things that we don't know about nuclear physics on the observables that are measured in experiments.
12. 07. 2018 at 14:00 S2 11/10	SFB Colloquium Zsolt Poldolyak (University of Surrey) Gamma-Ray Spectroscopy of Heavy Neutron-Rich Nuclei Information gained on neutron-rich N~126 nuclei is essential for the understanding of nuclear structure in heavy nuclei. Studies around doubly magic systems allow direct tests of the purity of shell model wave functions. From a longer-term perspective, experiments in this region pave the way toward the proposed nuclear-astrophysical r-process waiting point nuclei along the N = 126 shell closure. In the case of the beta decay of N~126 nuclei there is a competition between allowed and first-forbidden transitions. This is the mass region where first-forbidden (FF) transitions can be dominant, which can have profound implications on their half-lives and therefore on the r-process (A~195 abundance peak). Recently several experiments were performed at Gammasphere and ISOLDE with the aim to study neutron-rich nuclei around 208Pb. 1.) Structure of 208Tl from the beta decay of 208Hg. 208Tl being a one-proton-hole one-neutron-particle nucleus, its excited levels give direct information on the proton-neutron interaction in the Z<82, N>126 quadrant. In addition, the existence of both negative and positive parity states at low excitation energy makes this nucleus an ideal testing ground for the study of the competition between first-forbidden and allowed beta decay. 2.) Structure of 207Tl from the beta decay of 207Hg. A large number of excited states, several of them of octupole character were observed and compared with calculations. 3.) The high-spin structure of 207Tl was studied in deep-inelastic reactions. The talk will focus on recent results and their interpretation.
07. 06. 2018 at 14:00 S2 11/10	SFB Colloquium Brian Metzger (Columbia University) The Multi-Messenger Picture of a Neutron Star Merger On August 17 the LIGO/Virgo gravitational wave observatories detected the first binary neutron star merger event (GW170817), a discovery followed by the most ambitious electromagnetic (EM) follow-up campaign ever conducted. Within 2 seconds of the merger, a weak burst of gamma-rays was discovered by the Fermi and INTEGRAL satellites. Within 11 hours, a bright but rapidly-fading thermal optical counterpart was discovered in the galaxy NGC 4993 at a distance of only 130 Million light years. The properties of the optical transient match remarkably well predictions for "kilonova" emission powered by the radioactive decay of heavy nuclei synthesized in the expanding merger ejecta by rapid neutron capture nucleosynthesis (r-process). The rapid spectral evolution of the kilonova emission to near-infrared wavelengths demonstrates that a portion of the ejecta contains heavy lanthanide nuclei. Two weeks after the merger, rising non-thermal X-ray and radio emission were detected from the position of the optical transient, consistent with delayed synchrotron afterglow radiation from an initially off-axis relativistic jet (or a shock-heated "cocoon" produced as the ejecta interacts with the kilonova ejecta). I will describe efforts to create a unified scenario for the range of EM counterparts from GW170817 and their implications for the astrophysical origin of the r-process and the properties of neutron stars (particularly their uncertain radii and maximum mass, which are determined by the equation of state of dense nuclear matter). Time permitting, I will preview the upcoming era of multi-messenger astronomy, once Advanced LIGO/Virgo reach design sensitivity and a neutron star merger is detected every few weeks.
29. 05. 2018 at 14:00 S2 11/207	SFB Colloquium Luna Pellegri (Wits University/iThemba LABS) Nuclear physics news from the Southern Hemisphere The Pygmy Dipole Resonance (PDR), the low energy part of the electric dipole response in nuclei, is particularly relevant to investigate the nuclear structure and for its connections with photodisintegration reaction rates in astrophysical scenarios. Studies on the PDR are currently almost exclusively focused on spherical nuclei. For deformed nuclei several theoretical and experimental works have been performed to investigate the response of the Giant Dipole Resonance (GDR) while there are only a few on the PDR. iThemba LABS, South Africa, is a suitable laboratory for the experimental study of the PDR. The use of the high-energy resolution magnetic spectrometer coupled to an array of gamma-ray detectors is a perfect combination to investigate the nature of the PDR in detail. In particular, since very few measurements on the PDR have been performed in deformed nuclei up to now, a research activity was started in 2015 to provide such information. A structural support was developed to couple the gamma-ray detectors (BaGeL - Ball of Germanium and LaBr detectors) with the K600 magnetic spectrometer. The installation of the structure was completed in October 2016 and the first K600+BaGeL experiment was performed to study the electric response of Sm154 excited via inelastic scattering of alpha particles. The results of this experiment together with those performed using other reaction probes will provide new insights into the role of the deformation in the excitation of the PDR. A project to increase the gamma-ray detection efficiency of the iThemba LABS setup was recently funded by the South African National Research Foundation (NRF). This project will result in the extension of the gamma-ray detector array AFRODITE, up to 17 HPGe clover detectors, and in the construction of the African LaBr3:Ce Array (ALBA), an array of 23 large volume LaBr3:Ce. These arrays can be coupled to the K600 magnetic spectrometer and silicon detector arrays for gamma-particle coincidence measurements. This unique setup will allow for a new generation of experiments with a much-increased efficiency for detecting gamma decay compared to arrays currently available worldwide. Preliminary results of the PDR campaign as well as an overview on the iThemba LABS facilities will be given.
19. 04. 2018 at 15:15 S2 11/10	SFB Colloquium Francesco Cappuzzello (University of Catania) The nuclear matrix element of 0vbb decay and the NUMEN project at INFN-LNS The physics case of neutrino-less double beta decay and its tremendous implications on particle physics, cosmology and fundamental physics will be briefly introduced. In particular, the crucial aspect of the nuclear matrix elements entering in the expression of the half-life of this process will be deepened. The novel idea of using heavy-ion induced reactions as useful tools for the determination of these matrix elements will be then presented. The strengths and the limits of the proposed methodology will be indicated. New data from MAGNEX facility at the INFN-LNS laboratory give first evidences of the possibility to get quantitative results from experiments. Finally, the NUMEN project of INFN and the proposed strategy to this research will be sketched also in the view of the emerging technologies proposed.
08. 02. 2018 at 15:15 S2 11/10	SFB Colloquium Kei Minamisono (NSCL) Nuclear structure studies using lasers at NSCL/MSU Nuclear spin, electromagnetic moments and charge radius of radioactive nuclei are determined using laser spectroscopy techniques at the BEam COoling and LAser spectroscopy (BECOLA) facility at the National Superconducting Cyclotron Laboratory located in Michigan State University. The radioactive isotopes are produced using projectile-fragmentation reactions followed by in-flight separation and gas stopping. The scheme complements the reach over isotopes of ISOL-type facilities, where many laser spectroscopy data has been obtained for selected elements. BECOLA is currently the only laser spectroscopy facility that can accept radioactive beams from the fragmentation facility, and opens up new opportunities to explore key rare isotopes that have been difficult for laser spectroscopy to access before. I will introduce the BECOLA facility, and discuss recent results for neutron-deficient nuclei at the neutron shell closures N = 20 around Ca and N = 28 around Ni isotopes.
25. 01. 2018 at 15:15 S2 11/10	SFB Colloquium Michael Jentschel (Institut Laue-Langevin, Grenoble) Gamma ray spectroscopy at the institute Laue-Langevin The ILL operates one of the most intense neutron sources in the world. Although primarily used for neutron scattering there exist a long-standing history of gamma ray spectroscopy at the ILL. The availability of well collimated intense neutron beams and in-pile sample irradiation positions allowed to develop quite unique instruments and applications of gamma ray spectroscopy. The talk will start with giving an overview on the different aspects of neutron based gamma ray spectroscopy at the ILL. Amongst the operating gamma ray instruments the ultra-high-resolution gamma ray spectrometers GAMS play a particular role due to their outstanding energy resolution and dynamic range. The instruments are based on perfect crystal Laue diffraction of gamma rays produced by excited nuclei in the reactor and their operation requires one of the worlds best angle measurement devices. Accordingly the experiments contributed in the past to many different fields in physics: nuclear structure, metrology, photon matter interaction, crystallography and astrophysics. In a second part the talk will review some highlights from the past 20 years of operation of these instruments.
14. 12. 2017 at 14:00 S2 11/10	SFB Colloquium Hans-Thomas Janka (MPI Garching) 3D Core-Collapse Supernova Modelling and Applications to Cas A and other Supernova Remnants First three-dimensional, first-principle simulations of core-collapse supernovae have become possible in the recent past. They demonstrate the basic viability of the neutrino-driven mechanism for powering the explosions of the majority of supernova progenitors. Although a number of open questions remain to be settled, the explosion models are now sufficiently mature to strive for detailed comparisons against observations, for example considering well studied, nearby supernovae and supernova remnants. This talk will review our basic understanding of the explosion mechanism and report some results of such observational tests.
26. 10. 2017 at 14:00 S2 11/10	SFB Colloquium Aleksi Vuorinen (Helsinki Institute of Physics) Dense QCD matter from first principles Neutron stars, currently probed using both electromagnetic and gravitational wave observations, contain some of the densest matter in the known universe, possibly including even deconfined quark matter. In my talk, I will describe recent efforts to understand the collective properties of high-density quark matter, using both resummed perturbation theory and the holographic AdS/CFT duality. Prospects for quantitatively constraining the observable properties of neutron stars using these results will also be discussed in detail.
13. 07. 2017 at 15:15 S2 11/10	SFB Colloquium Kei Kotake (Fukuoka University/Japan) Muli-messenger predictions from multi-D core-collapse supernova models (with refined neutrino reactions in progress) We will report status of multi-messenger predictions from our 2D and 3D core-collapse supernova (SN) models. After some review about SN multi-messengers, we show that progenitor's core-compactness is a good diagnostics for predicting gravitational-wave (GW) signals and also diffuse-supernova-neutrino-background (DSNB) signals. From our 3D rotating models, we show some interesting viewing-angle effects of the neutrino and GW signals. Finally we report our on-going project to update neutrino opacities in our work-horse supernova code.
28. 06. 2017 at 11:00 S2 08/171	SFB Colloquium Sharon McGrayne (SFB 1245 Women's Week) From Maria Goeppert Mayer to today, and what research suggests can be done When my first book Nobel Prize Women in Science was published in 1993, the legal barriers against women in academic science seemed to be fading into the past. But now we realize that subtle barriers are also difficult to deal with. In my talk, I'll give some examples, past and present, and describe recent research on the subject. In particular, I will draw on what I've learned from the writing a book about the present situation for women in science with Dr. Rita Colwell, microbiologist, former director of the National Science Foundation, and Distinguished Professor at the University of Maryland, College Park, and Johns Hopkins University.
18. 05. 2017 at 15:30 S2 11/207	SFB Colloquium Paul-Gerhard Reinhard (Uni Erlangen) Nuclear density-functional theory - from photo-absorption strength to bulk Self-consistent nuclear models are based on energy-density functional adjusted to a reference set of nuclear data. The talk concentrates on the most widely used Skyrme- Hartree-Fock (SHF) approach comparing occasionally with the relativistic mean-field model. The first part of the talk gives an introductory overview illustrating the wide range of phenomena which can be described by static and dynamics SHF. The second part explains the empirical calibration of the energy functional by least-squares fits and discusses how statistical analysis, related to the least-squares method, allows to estimate extrapolation uncertainties and correlations between different observables. The third part discusses as application response properties of finite nuclei (giant resonances, polarizability) and extrapolations to neutron matter. It works out the connections between the equation of state of bulk matter and the response observables. This way one can estimate the relation between quality of data in finite-nuclei and predictions on star matter. Particularly the dipole polarizability plays a crucial role in neutron matter.
09. 02. 2017 at 15:15 S2 11/10	SFB Colloquium Thomas Luu () Applying Lattice QCD techniques to low-dimensional non-relativistic systems I discuss the application of lattice monte carlo (MC) techniques to calculate the properties of low-dimensional non-relativistic systems. For specific applications I consider the 2-dimensional graphene and quasi 1-dimensional carbon nanotube systems at half-filling with strongly correlated electrons. I compare and contrast the use of MC techniques in lattice QCD with these low-dimensional non-relativistic systems, and show how lattice QCD techniques can be applied to calculate the quasi-particle spectrum of these systems. I discuss the limitations of this formalism, and conclude with an outlook of possible future calculations.
26. 01. 2017 at 15:15 S2 11/10	SFB Colloquium Barbara Dietz (Lanzhou University/China) Chaos and Regularity in the Doubly Magic Nucleus 208Pb High resolution experiments have recently lead to a complete identification (energy, spin, and parity) of 151 nuclear levels up to an excitation Energy of Ex= 6.20 MeV in 208Pb. We present a thorough study of the fluctuation properties in the energy spectra of the unprecedented set of nuclear bound states. In a first approach we grouped states with the same spin and parity into 14 subspectra, analyzed standard statistical measures for short- and long-range correlations and then computed their ensemble average. Their comparison with a random matrix ensemble which interpolates between Poisson statistics expected for regular systems and the Gaussian Orthogonal Ensemble (GOE) predicted for chaotic systems shows that the data are well described by the GOE. In a second approach, following an idea of Rosenzweig and Porter we considered the complete spectrum composed of the independent subspectra. We analyzed their fluctuation properties using the method of Bayesian inference involving a quantitative measure, called the chaoticity parameter f, which also interpolates between Poisson (f=0) and GOE statistics (f=1). It turns out to be f~0.9. This is so far the closest agreement with GOE observed in spectra of bound states in a nucleus. The same analysis has also been performed with spectra computed on the basis of shell model calculations with different interactions (SDI, KB, M3Y). While the simple SDI exhibits features typical for nuclear many-body systems with regular dynamics, the other, more realistic interactions yield chaoticity parameters f close to the experimental values.
24. 11. 2016 at 15:20 S2 11/10	SFB Colloquium Pierre Capel () Past, present and future of the eikonal description of reactions involving exotic nuclei Away from the valley of stability, a numerous of exotic nuclear structures are encountered: shell inversions, halo nuclei,... The study of these short-lived exotic systems is mostly performed through nuclear reactions measured at Radioactive-Ion Beam facilities. To infer valuable structure information from experimental data, a reliable model of the reaction mechanism coupled to a realistic description of the nucleus under investigation is required. The Dynamical Eikonal Approximation (DEA) is such a model for reactions involving one-nucleon halo nuclei. It has shown to provide excellent results for all kinds of observables when compared to experiments with both one-neutron (e.g. 11Be, 15C) and one-proton (8B) halo nuclei. It is hence an accurate tool to analyse reactions measured with exotic loosely-bound nuclei. However, as every model, the DEA has its own range of validity: it is mostly limited to intermediate or high beam energy. Moreover, the projectile description considered within the DEA remains simple: a valence nucleon bound to an inter core. During this seminar, I will review the DEA, show how it compares to other, more sophisticated, reaction models, and describe its successes in the analysis of exotic nuclear structures. I will also present what is planned in the future to extend its range of validity both in the reaction part and in the description of the projectile.
03. 11. 2016 at 15:20 S2 11/10	SFB Colloquium Xiaofei Yang (KU Leuven) Nuclear structure studies by the measurement of nuclear spins, moments and charge radii via laser spectroscopy techniques High resolution laser spectroscopy can access to multiple nuclear properties of ground/isomeric states of radioactive nuclei far from stability, such as nuclear spins, nuclear magnetic and quadruple moments and charge radii [1]. These fundamental properties of exotic nuclei provide important information for the investigation of the nuclear structure in different regions of nuclear chart. Currently, two complementary collinear laser spectroscopy set-ups are available at ISOLDE, Collinear Laser Spectroscopy (COLLAPS) and Collinear Resonant Ionization Spectroscopy (CRIS) [2]. Combining these two techniques, the nuclear structure in several key regions of the nuclear chart can be investigated, for example the structure of neutron-rich isotopes in the Ca region and in the Ni region, which just happens to be my research interest. Currently, several experiments are focusing on nuclear structure studies in these two regions [3-5]. In this talk, after an introduction of both the COLLAPS and CRIS techniques, I will mainly focus on my research interest on neutron-rich K[4], Sc[4] and Zn[3], Ge[5] isotopes using both experimental techniques. The results of nuclear spins, moments and charge radii of Zn isotopes, achieved from COLLAPS experiments, will be presented in details together with all the physics discussion [3]. For others, the physics motivation of each individual experiment and the status of the experiments will be introduced [4,5]. References: [1] P. Campbell et al., Progress in Particle and Nuclear Physics 86, 127 (2016). [2] http://collaps.web.cern.ch/ and http://isolde-cris.web.cern.ch/isolde-cris/ [3] X. F. Yang et al., Phys.Rev.Lett. 116, 182502 (2016); C.Wraith and X.F.Yang et al., in Preparation for Phys. Let. B (2016); L. Xie and X. F Yang et al,m In preparation for Phys. Rev. C (2016) [4]X.F. Yang et al., CERN-INTC-2016-008/INTC-P-458, X.F. Yang et al., CERN-INTC-2015-051/INTC-P-451 ; X.F. Yang et al., CERN-INTC-2015-050/INTC-P-450 ; [5]M.Bissell,X.F.Yang et al., CERN-INTC-2016-035/INTC-P-472 ; X.F.Yang, M.Bissel et al., CERN-INTC-2016-036/INTC-I-170.
14. 07. 2016 at 14:00 S2 11/10	SFB Colloquium (Argonne National Laboratory) Laser Probing of Simple Atoms, Exotic Nuclei The atomic structure of simple, few electron systems can be precisely calculated. Likewise, few nucleon systems can be accurately treated within ab-initio nuclear theories. Bringing these two fields together, we perform precision studies of light, radioactive isotopes that show a remarkable range of neutron-to-proton ratios. Techniques of high-resolution laser spectroscopy and of laser cooling and trapping offer unique access to precision nuclear structure and weak interaction studies of these isotopes to probe nucleon-nucleon interactions and to search for physics beyond the Standard Model. In my talk I will cover two on-going efforts in this direction: precision measurements of nuclear charge radii moving towards the proton rich Boron-8 and a beta-neutrino angular correlation measurement with laser trapped Helium-6.

Address

Technische Universität Darmstadt

Institut für Kernphysik
Theoriezentrum

S2|11
Schlossgartenstraße 2
64289 Darmstadt

Secretary

Stephanie Müller

+49 6151 16 21558
+49 6151 16 21555
stephanie.mueller@physik.tu-...