Scientific Colloquium Webinars 2021 (past)

Monday, 11/10 (16h, CET): hosted by GdR RESANET
A short History of Nuclear Astrophysics: Part II: The origin of the elements
Nikos PRANTZOS (IAP Paris)

I will present the second part of this Short history of Nuclear astrophysics, showing how the debate oscillated in the 1930ies and 1940ies between a primordial and a stellar origin of the chemical elements in the Universe. The former was promoted mainly by George Gamow and the latter by Fred Hoyle. The debate was settled in the mid-1950ies, after Burbidge, Burbidge, Fowler and Hoyle established the – rather long – list of nuclear processes that produce the majority of elements inside stars. However, more than 60 years later, several aspects of this ambitious project remain poorly understood yet.

Monday, 13/09 (16h, CET): hosted by GdR RESANET
Towards super heavy elements in France!
Barbara SULIGNANO (IRFU Saclay)

The ambitious scientific program to produce and study super heavy nuclei or neutron deficient nuclei close to the proton drip-line via fusion evaporation has led to the development of a new separator spectrometer: S3. The Super Separator Spectrometer (S3) facility is developed in the framework of the SPIRAL2 project. S3 has been designed to perform experiments with extremely low cross sections, taking advantage of the very high intensity stable beams of the superconducting linear accelerator of SPIRAL2.
The development of S3 has required to overcome multiple technological challenges: the construction of a powerful recoil separator with high mass resolution and large transmission capabilities; a high efficiency detection systems; a target able to support the high intense heavy ion-beams needed to access very low cross section reactions (picobarn). S3 is now in its final phase of construction and will soon be operational. In parallel, SIRIUS, a new focal plane detector has been developed, in order to detect rare ions such as super heavy elements.
In this talk will be presented the status of the project, the comparison with the different world laboratories where the production of super heavy elements is now possible and the physics intended to be performed in the next future.
The pdf of the talk is here.

Monday, 05/07 (16h, CET): hosted by GdR RESANET
Description of complex quantum systems with quantum computers,
Denis LACROIX (IJCLab Orsay)

With the arrival of the first quantum computer demonstrators, such as those developed by IBM or Google, the field of quantum computing (QC) is rapidly gaining interest and visibility. Programming on such quantum computer prototypes is still a formidable challenge, especially since they represent a disruptive technology, as widely expected. In the first part of my talk, I will make a very general introduction on quantum computing. The notion of qubits, quantum gates and circuits as well as the entanglement will be discussed. I will also briefly summarize the recent progress in quantum computer technologies and associated quantum processor units. Some resources for beginners on QC can be found at the QC2I project webpage [1]. 
In the second part of my talks, I will give examples of recent applications on the problem of  interacting particles that could be relevant not only for nuclear physics but also for other fields of physics and chemistry. I will show how superfluid systems can be encoded on a quantum computer. Two aspects will be discussed (i) the possibility to break and restore symmetries in QC [2] and (ii) the possibility to predicts eigenstates and long-time evolution from short time simulation on quantum computers [3].
[1] QC2I (quantum computing for the two infinities)
[2] Denis Lacroix,  “Symmetry-Assisted Preparation of Entangled Many-Body States on a Quantum Computer”, Phys. Rev. Lett. 125, 230502 (2020).
[3] Edgar-Andres Ruiz-Guzman and Denis Lacroix, “Predicting ground state, excited states and long-time evolution of many-body systems from short-time evolution on a quantum computer”, arxiv: 2104.08181

Monday, 21/06 (16h, CET): hosted by GdR RESANET
A short History of Nuclear Astrophysics: Part I: The Energy of Stars
Nikos PRANTZOS (IAP Paris)

I will present an overview of the development of nuclear astrophysics, from its beginnings in the late 1920s, till its maturation in the late 1960s. Nuclear astrophysics emerged from the « marriage » of the old science of astronomy with the young discipline of nuclear physics, with a twofold objective: to understand the energy of the Sun and stars and the origin of the chemical elements in the Universe. Its development is intimately connected to the development of particle physics during its early period. Its history is the result of the work of some of the greatest physicists of the 20th century and it was crowned by two Nobel prizes. In the first part I will present our progressive understanding of the source of stellar energy, which was completed in the late 1930s.
In an era of evergrowing specialisation in all scientific disciplines, it is useful for students and scientists alike to gain an elementary knowledge of the history of ideas and of their development in the socio-cultural and technological context of their epoch.
The pdf of the talk is here.

Monday, 07/06 (16h, CET): hosted by GdR RESANET
New insights into fission from recent experiments: What drives fission across the nuclear chart?
Christelle SCHMITT (IPHC Strasbourg)

Nuclear fission owes its name by the fact that it resembles the division of living cells. But hidden behind is the complex re-arrangement of a many-body quantum system involving two types of nucleons, the protons and the neutrons. As a consequence, the process revealed to be a rich laboratory for studying fundamental nuclear properties, in general, and dynamical aspects of nuclear reactions, in particular. The importance of fission in astrophysics and for a wide variety of societal applications is established also.
Several probes have been proposed to study fission. In this presentation, we focus on the characterization of the fission-fragment products in terms of mass, charge and energy, and on their de-excitation. Recent experimental advances in the region of actinides and neutron- deficient lead are used to demonstrate the step forward in the field made from most accurate measurements. A consistent analysis of the information collected during the last years shows that the protons – which importance was overlooked so far, are key drivers of fission over the nuclear chart. A brief discussion of state-of-the-art models is finally proposed, emphasizing the necessary theoretical development regarding the dynamical transition from a fissioning-system- to a nascent-fragment-driven process.

Monday, 10/05 (16h, CET): hosted by GdR RESANET
Search for new physics beyond the Standard Model with precision measurements in nuclear beta decays,
Etienne LIENARD (LPC Caen)

Precision measurements in nuclear beta decays provide sensitive tools to test the foundations and symmetries of the Standard electroweak Model and to search for exotic couplings presently excluded by the V-A theory in processes involving the lightest quarks. The main aim of such measurements is to highlight deviations from the Standard Model predictions as possible indications of new physics, complementing other searches at large-scale facilities such as the LHC. The sensitive parameters are often deduced from correlation studies between the very few bodies involved in the decay. This requires to perform very precise measurements using advanced technical methods, such as ion or atom traps installed on-line in radioactive nuclei production facilities. Data analysis also requires generating the most realistic simulations to take into account the relevant parameters of the experimental setup and their systematic effects on the measured quantities.
In this seminar, I will present different experimental projects in which LPC Caen is involved, starting from the development of LPCTrap at GANIL to search for exotic tensor currents in the decay of 6 He 1+ ions. This pioneer experiment laid the foundations of our present projects, not only in the search for exotic currents (WISArD, b-STILED), but also with other perspectives comprising the test of CVC from the study of mirror transitions and the quest for new sources of CP violation (MORA) needed to explain the large matter-antimatter asymmetry observed in the universe. The status and goals of these projects will be discussed.

Monday, 26/04 (16h, CET): hosted by CENBG
Precision mass measurements for nuclear and neutrino physics studies

Klaus BLAUM (Max-Planck-Institut für Kernphysik, Heidelberg)

Rapidly developing neutrino physics has found in Penning-trap mass spectrometry a staunch ally in investigating and contributing to a variety of fundamental problems. The most familiar are the absolute neutrino mass and the possible existence of resonant neutrinoless double-electron capture / double-beta dacay and of keV-sterile neutrinos. This review provides an overview on the latest achievements and future perspectives of Penning-trap mass spectrometry on short-lived as well as stable nuclides with applications in nuclear structure, neutrino physics and most recently even in dark matter searches where relative mass uncertainties at the level of 10-11 and below are required.
The pdf of the talk is here.

Monday, 12/04 (16h, CET):
From nuclei to neutron stars: Combining nuclear physics and multi-messenger observations
Ingo TEWS (Los Alamos National Laboratory, USA)

Neutron stars contain the largest reservoirs of degenerate fermions, reaching the highest densities we can observe in the cosmos, and probe matter under conditions that cannot be recreated in terrestrial experiments. Throughout the Universe, a large number of high-energy, cataclysmic astrophysical collisions of neutron stars are continuously occurring. These collisions provide an excellent testbed to probe the properties of matter at densities exceeding the density inside atomic nuclei, are an important site for the production of elements heavier than iron, and allow for an independent measurement of the expansion rate of our Universe.
To understand these remarkable events, reliable nuclear-physics input is essential. In this colloquium, I will review how to use state-of-the-art nuclear-physics calculations to provide a consistent and systematic approach to strongly interacting systems from nuclei to neutron stars with theoretical uncertainties.  I will discuss nuclear-physics predictions for the dense nucleonic matter relevant for neutron stars, and discuss how astrophysical multi-messenger observations of neutron stars and their mergers can be used to further elucidate the properties of matter under extreme conditions.
The pdf of the talk is here. LA-UR-21-23129

Monday, 29/03 (16h, CET): hosted by GdR RESANET
Selected topics on heavy and super-heavy nuclei,
Christophe THEISEN (DPhN Saclay)

In this webinar I will review selected aspects of heavy and superheavy nuclei, starting from the discovery of transactinide nuclei in the 40th using neutron « beams ». Then, still with neutrons, I will continue with the question of the superheavy nuclei nucleosynthesis in the r-process: supernovae explosions, neutron star mergers, collapsars. These nucleosynthesis processes are strongly constrained by nuclear structure, and in particular by the fission barriers, for nuclei where no experimental data can be obtained. I will therefore discuss theoretical predictions, both for spherical magic and deformed regions. We will see how we can obtain experimentally information on not-too-heavy nuclei near the deformed shell gap Z=100 N=152. How can we deduce and in some cases measure the deformation or the electric quadrupole moment of the heaviest nuclei (spectroscopy, coulex, laser spectroscopy)? I will also discuss the theoretical difficulties and problems faced in this region. I will conclude with few flagship experimental projects such as S3 and the future NEWGAIN injector at GANIL, the possibility of re-accelerating actinide nuclei, and the synthesis using multi-nucleon transfer reactions. 
The pdf of the talk is here.

Monday, 15/03 (16h, CET): hosted by GdR RESANET
On the tracks of two-proton radioactivity,
Jérôme GIOVINAZZO (CENBG Bordeaux)

The two-proton radioactivity is a very exotic decay mode that can occur for very neutron deficient nuclei located beyond proton drip-line. From theoretical assumptions, it was already predicted in the early 1960’, together with the one-proton radioactivity. Nevertheless, it is only in the years 2000 that a first experimental indication of the phenomenon could be observed, thanks to the development of the facilities that can produce nuclei far from stability.
This process is made possible thanks to very specific quantum effects at the microscopic level: the Coulomb barrier originating in the electric charge of all protons in the nucleus and the gain of stability caused by the coupling of nucleons in pairs. It has been observed in the decay of only 4 nuclei, and 20 years after the first observation, in order to understand this radioactivity, new experimental tools are built to measure the correlations of the protons, and theoretical models are developed to describe both the structure of the emitting nuclei and the dynamics of the emission.
In this presentation will give a brief description of this exotic decay process and explain the major steps of its study, from both theoretical and experimental sides.
The pdf of the talk is here.

Organizers:P. Ascher (CENBG Bordeaux), O. Dorvaux (IPHC Strasbourg), S. Diglio (SUBATECH Nantes), J. Dudouet (IP2I Lyon), A. Fantina (GANIL Caen), G. Henning (IPHC Strasbourg), A. Korichi (IJCLab Orsay), O. Lopez (LPC Caen), J. Margueron (IP2I Lyon), G. Quemener (LPC Caen), O. Sorlin (GANIL Caen), B. Sulignano (IRFU Saclay), J.-C. Thomas (GANIL Caen), L. Thulliez (IRFU Saclay), A. Uras (IP2I Lyon), M. Vandebrouck (IRFU Saclay), P. Van Hove (IPHC Strasbourg), G. Verde (L2IT Toulouse).