Institut für Kernphysik
Theoriezentrum

Kolloquium des SFB 1245

Ort: S2|11, Raum 10

06.07.2023
14:00
S2|11 10 		Prof. Dr. Dean Lee (Michigan State University and FRIB)
Nuclear Structure and Thermodynamics from Nuclear Lattice Effective Field Theory
Nuclear lattice effective field theory combines Monte Carlo lattice simulations with the theoretical framework of effective field theory. After a general introduction to the approach, I discuss several recent results on the cluster structure of the low-lying states of carbon-12, binding energies and charge radii of light and medium-mass nuclei, the liquid-vapor critical point in symmetric nuclear matter, light cluster abundances in hot dilute nuclear matter, and spin and density correlations in hot neutron matter relevant for neutrino scattering.
04.05.2023
14:00
S2|11 10 		Dr. Gaute Hagen (Oak Ridge National Laboratory)
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
14:00
S2|11 10 		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
14:00
S2|11 10 plus Zoom 		Dr. 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
14:00
S2|11 10 plus Zoom 		Iris Dillmann (TRIUMF)
The TRISR Project – A Storage Ring for Neutron Capture 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
14:00
S2|11 10 plus Zoom 		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
10:30
Zoom 		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
14:00
Zoom 		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
14:00
Zoom 		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
14:00
Zoom 		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
14:00
Zoom 		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
14:00
Zoom 		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
14:00
S2|11 10 		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
15:15
S2|11 10 		Valentin Nesterenko (Dubna)
Vortical excitations in nuclei
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
10:00
S2|11 10 		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.