Mapping the tower of nuclear Effective Field Theory
The ability of nuclear models to accurately predict the rich phenomenology emerging in nuclei (whether for fundamental purposes or nuclear data applications) is conditioned by the possibility to construct a systematically improvable theoretical framework, i.e. with controlled approximations and estimation of associated uncertainties and biases. This is the goal of so called ab initio methods, which rely on two steps:
1 - The construction of an inter-nucleon interaction in adequation with the underlying theory (quantum chromodynamics) and adjusted in small systems, following effective field theory paradigm.
2 - The resolution of nuclear many-body problem to a given accuracy (for structure or reactions observables). This provides predictions in all nuclei of interest and includes the uncertainty propagation stemming from the interaction model up to nuclear data predictions.
This PhD thesis mostly deals with Step 1. The goal of the thesis is to construct a family of ab initio interactions by developing a new adjustment procedure of the low energy constants (including the evaluation of covariances for sensitivity analysis). The adjustment will include structure data but also reaction observables in light systems. This will open the door to a new evaluation of p+n->d+gamma cross sections (which have large uncertainties despite their importance for neutronics applications) in the context of state-of-the-art effective fields theories.
The thesis will be done in collaboration between CEA/IRESNE (Cadarache) and IJCLab (Orsay), the PhD student will spend 18 months in each laboratories. Professional perspectives are academic research and R&D labs in nuclear physics.
MEASUREMENT OF THE W-BOSON MASS WITH THE ATLAS DETECTOR AT THE LHC
The objective of the thesis is a precise measurement of the mass and width of the W boson, by studying its leptonic decays with the ATLAS detector at the LHC. The analysis will be based on data from Run 2 of the LHC, and aims for an precision on the mass of 10 MeV.
The candidate will be involved in the study of the alignment and calibration of the ATLAS muon spectrometer. IRFU played a leading role in the design and construction of this instrument and is heavily involved in its scientific exploitation. This will involve optimally combining the measurement given by the spectrometer with that of the ATLAS inner detector, using a precise model of the magnetic field and the relative positioning of these systems, in order to reconstruct the muon kinematics with the precision required for measurement.
The second phase of the project consists of improving the modeling of the W-boson production and decay process and optimizing the analysis itself in order to minimize the final uncertainty of the measurement. The measurement result will be combined with other existing measurements, and interpreted in terms of compatibility with the Standard Model prediction or as an indication of the presence of new physics.
Magnetic fusion turbulence: where do reduced models fail, how to enrich them?
One of the key challenges facing the field of fusion plasma modeling is the nonlinear nature of the plasma response. This means that factors such as temperature and density gradients, flows, and velocity gradients all have an impact on the transport of heat, particles, and momentum in complex ways. Modeling such a system requires a range of approaches, from the highly detailed flux-driven gyrokinetics method to simpler quasilinear models within an integrated framework. These have proven effective in interpreting experimental data and predicting plasma behaviour. However, there are two significant challenges to this approach. Firstly, modeling the peripheral region of the plasma edge, at the transition between open and closed field lines, is challenging due to the confluence of significantly different underlying physics. Recent research indicates that current quasilinear transport models may have significant shortcomings in this region. Secondly, modeling the 'near marginality' regime is challenging due to the fact that it involves a state of dynamic equilibrium where the system's behaviour is self-regulated by slow, large-scale modes. Computing this state is challenging and requires a flux-driven gyrokinetic approach to move away from the typical assumption of time scale separation between turbulence and transport. Recent work from within our team indicates that current quasilinear transport models may also be facing significant shortcomings in this regime. It is crucial to understand this regime in depth as it is relevant for future machine operation. We are now in a position to address these two issues, as we have access to cutting-edge in-house tools relevant to both ends of the spectrum.
We plan to compare transport predictions in the edge and near marginality regimes from the advanced flux-driven gyrokinetic code GYSELA with those from the integrated framework using the reduced quasilinear QuaLiKiz model. The research will contribute to the development of robust reduced models for transport, crucial for the interpretation of current experimental data and for future burning plasma operation.