Towards a high spatial resolution pixel detector for particle identification: new detectors contribution to physics
Future experiments on linear colliders (e+e-) with low hadronic background require improvements in the spatial resolution of pixel vertex detectors to the micron range, in order to determine precisely the primary and secondary vertices for particles with a high transverse momentum. This kind of detector is set closest to the interaction point. This will provide the opportunity to make precision lifetime measurements of short-lived charged particles. We need to develop pixels arrays with a pixel dimension below the micron squared. The proposed technologies (DOTPIX: Quantum Dot Pixels) should give a significant advance in particle tracking and vertexing. Although the principle of these new devices has been already been studied in IRFU (see reference), this doctoral work should focus on the study of real devices which should then be fabricated using nanotechnologies in collaboration with other Institutes. This should require the use of simulation codes and the fabrication of test structures. Applications outside basics physics are X ray imaging and optimum resolution sensors for visible light holographic cameras.
The galaxy clusters in the XMM-Euclid FornaX deep field
The XMM Heritage project on the DEEP Euclid Fornax field aims to characterize distant galaxy clusters by comparing X-ray and optical/IR detections. The two methods call on very different cluster properties; ultimately, their combination will make it possible to set the free parameters of the Euclid cluster selection function over the entire WIDE survey, and thus constitute a fundamental ingredient for Euclid cosmological analysis.
The targeted redshift range ([1-2]) has never been systematically explored, despite being a critical area for the use of clusters in cosmology.
With FornaX, for the first time we'll have access to a large volume at these redshifts, enabling us to statistically quantify the evolution of clusters: role of AGNs in the properties of intracluster gas? Are there massive gas-deficient clusters? What are the respective biases of X-ray and optical detection?
The thesis work will involve (1) building and validating the X-ray cluster catalog; (2) correlating it with the optical/IR catalogs obtained by Euclid; and (3) studying the combined X-ray and optical evolution of the clusters.
All the algorithms for detecting and characterizing clusters in XMM images already exist, but we'll be pushing detection even further by using artificial intelligence techniques (combining spatial and spectral information on sources).
The complex problem of spatial correlation between XMM and Euclid cluster catalogs will also involve AI.
Project website: https://fornax.cosmostat.org/
DEVELOPMENT OF AN AI-BASED FRAMEWORK IN NEUTRINO PHYSICS: A FOCUS ON TIME SERIES EVENT RECONSTRUCTION AND MULTIVARIATE SCIENCE ANALYSES
Neutrinoless double beta decay (0nßß) represents a pivotal area of research in nuclear physics, offering profound insights into neutrino properties and the potential violation of lepton number conservation. The CUPID experiment is at the forefront of this investigation, employing advanced scintillating bolometers at cryogenic temperatures to minimize radioactive background noise. It aims to achieve unprecedented sensitivity in detecting 0nßß decay using lithium molybdate (Li2MoO4) crystals. These crystals are particularly advantageous due to their scintillation properties and the high Q-value of the decay process, which lies above most environmental gamma backgrounds. In turn this endeavour will require operating a fine grained array of 1596 dual heat/light detectors with excellent energy resolution. The proposed thesis integrates artificial intelligence (AI) techniques to enhance data analysis, reconstruction, and modeling for the CUPID experiment demonstrators and the science exploitation of CUPID.
The thesis will focus on two primary objectives:
1. Improved Time Series Event Reconstruction Techniques
- CNN based denoising and comparison against optimal classical techniques
2. Multivariate science analysis of a large neutrino detector array
- Analysis of Excited States: The study will use Geant4 simulations together with the CUPID background model as training data to optimize the event classification and hence science potential for the analysis of 2nßß decay to excited states.
Probing Gluon Dynamics in the Proton via the Exclusive Phi Meson Photoproduction with CLAS12
Protons and neutrons are made of partons (quarks and gluons) that interact via the strong force, governed by Quantum Chromodynamics (QCD). While QCD can be computed at high energies, its complexity reveals itself at low energies, requiring experimental inputs to understand nucleon properties like their mass and spin. The experimental extraction of the Generalized Parton Distributions (GPDs), which describe the correlation of the partons longitudinal momenta and transverse positions within nucleons, provide critical insights into these fundamental properties.
This thesis focuses on analyzing data from the CLAS12 detector, an experiment part of Jefferson Lab's research infrastructure, one the 17 National Laboratory in the USA. CLAS12, a 15-meter-long fixed-target detector with large acceptance, is dedicated to hadronic physics, particularly GPDs extraction. The selected student will study the exclusive photoproduction of the phi meson (gamma p->phi p’), which is sensitive to gluon GPDs, still largely unexplored. The student will develop a framework to study this reaction in the leptonic decay channel (phi -> e+e-) and develop a novel Graph Neural Network-based algorithm to enhance the scattered proton detection efficiency.
The thesis will aim at extracting the cross section of the photoproduction of the phi, and interpret it in term of the proton's internal mass distribution. Hosted at the Laboratory of Nucleon Structure (LSN) at CEA/Irfu in Saclay, this project involves international collaboration within the CLAS collaboration, travel to Jefferson Lab for data collection, and presentations at conferences. Proficiency in particle physics, programming (C++/Python), and English is required. Basic knowledge of particle detectors and Mahine Learning is advantageous but not mandatory.
Search for new physics through resonant di-Higgs production
Since the discovery of the Higgs boson (H) in 2012 by the ATLAS and CMS experiments, and after more than 10 years of studying its properties, especially thanks to the large Run 2 datasets from the LHC collected by both collaborations between 2015 and 2018, everything seems to indicate that we have finally completed the Standard Model (SM), as it was predicted sixty years ago. However, despite the success of this theory, many questions remain unanswered, and in-depth studies of the scalar sector of the SM could provide us with hints about how to address them.
The study of double Higgs boson (HH) production is currently of particular interest to the high-energy physics community, as it constitutes the best experimental handle to access the H self coupling, and consequently the Higgs potential V(H). Due to its direct links with the electroweak phase transition (EWPT), the shape of V(H) is particularly relevant for beyond the Standard Model (BSM) theories that attempt, for instance, to explain primordial baryogenesis and the matter-antimatter asymmetry in our universe. Some of these models predict an expanded scalar sector, involving the existence of additional Higgs bosons, often interacting preferentially with the SM Higgs.
The CMS group at CEA-Saclay/IRFU/DPhP therefore wishes to offer a PhD position focused on the search for resonant HH production, concentrating on the H(bb)H(tautau) channel, with the aim of constraining these models, for the first time involving a complete characterization of the BSM signal and its interferences with the SM. The selected student would participate in well-established research activities within the CMS collaboration and the CEA group, in connection with several institutes in France and abroad.
Near-threshold phenomena in nuclear structure and reactions
It is proposed to study the salient effects of coupling between discrete and continuous states near various particle emission thresholds using the shell model in the complex energy plane. This model provides the unitary formulation of a standard shell model within the framework of the open quantum system for the description of well bound, weakly bound and unbound nuclear states.
Recent studies have demonstrated the importance of the residual correlation energy of coupling to the states of the continuum for the understanding of eigenstates, their energy and decay modes, in the vicinity of the reaction channels. This residual energy has not yet been studied in detail. The studies of this thesis will deepen our understanding of the structural effects induced by coupling to the continuum and will provide support for experimental studies at GANIL and elsewhere.
Fast parameter inference of gravitational waves for the LISA space mission
Context
In 2016, the announcement of the first direct detection of gravitational waves ushered in an era in which the universe will be probed in an unprecedented way. At the same time, the complete success of the LISA Pathfinder mission validated certain technologies selected for the LISA (Laser Interferometer Space Antenna) project. The year 2024 started with the adoption of the LISA mission by the European Space Agency (ESA) and NASA. This unprecedented gravitational wave space observatory will consist of three satellites 2.5 million kilometres apart and will enable the direct detection of gravitational waves at undetectable frequencies by terrestrial interferometers. ESA plans a launch in 2035.
In parallel with the technical aspects, the LISA mission introduces several data analysis challenges that need to be addressed for the mission’s success. The mission needs to prove that with simulations, the scientific community will be able to identify and characterise the detected gravitational wave signals. Data analysis involves various stages, one of which is the rapid analysis pipeline, whose role is to detect new events and characterise the detected events. The last point concerns the rapid estimation of the position in the sky of the source of gravitational wave emission and their characteristic time, such as the coalescence time for a black hole merger.
These analysis tools form the low-latency analysis pipeline. As well as being of interest to LISA, this pipeline also plays a vital role in enabling multi-messenger astronomy, consisting of rapidly monitoring events detected by electromagnetic observations (ground-based or space-based observatories, from radio waves to Gamma rays).
PhD project
The PhD project focuses on the development of event detection and identification tools for the low-latency alert pipeline (LLAP) of LISA. This pipeline will be an essential part of the LISA analysis workflow, providing a rapid detection of massive black hole binaries, as well as a fast and accurate estimation of the sources’ sky localizations as well as coalescence time. These are key information for multi-messager follow-ups as well as for the global analysis of the LISA data.
While rapid analysis methods have been developed for ground-based interferometers, the case of space-based interferometers such as LISA remains a field to be explored. Adapted data processing will have to consider how data is transmitted in packets, making it necessary to detect events from incomplete data. Using data marred by artefacts such as glitches or missing data packages, these methods should enable the detection, discrimination and analysis of various sources: black hole mergers, EMRIs (spiral binaries with extreme mass ratios), bursts and binaries from compact objects. A final and crucial element of complexity is the speed of analysis, which constitutes a strong constraint on the methods to be developed.
To this end, the problems we will be tackling during this thesis will be:
1. The fast parameter inference of the gravitational waves, noticeably, the sky position, and the coalescence time. Two of the main difficulties reside in the multimodality of the posterior probability distribution of the target parameters and the stringent computing time requirements. To that end, we will consider different advanced inference strategies including:
(a) Using gradient-based sampling algorithms like Langevin diffusions or Hamiltonian Monte Carlo methods adapted to LISA’s gravitational wave problem,
(b) Using machine learning-assisted methods to accelerate the sampling (e.g. normalising flows),
(c) Using variational inference techniques.
2. The early detection of black hole mergers.
3. The increasing complexity of LISA data, including, among others, realistic noise, realistic instrument response, glitches, data gaps, and overlapping sources.
4. The online handling of the incoming 5-minute data packages with the developed fast inference framework.
This thesis will be based on applying Bayesian and statistical methods for data analysis and machine learning. However, an effort on the physics part is necessary, both to understand the simulations and the different waveforms considered (with their underlying hypotheses) and to interpret the results regarding the detectability of black hole merger signals in the context of the rapid analysis of LISA data.
NEW PATHS TO PRODUCE NEUTRON RICH HEAVY NUCLEI
One of the strongest research projects in recent years has emerged from a critical, unresolved question about the natural origin of nuclei heavier than iron. The closed neutron shell, N = 126, as the final waiting point in the r-process (rapid neutron capture process), plays an essential role in the formation of these nuclei. However, recent efforts to synthesize superheavy elements and explore N = 126 neutron-rich nuclei have faced significant challenges due to extremely low cross sections using traditional fusion-evaporation reactions.
These factors highlight the urgent need for alternative reaction mechanisms. One alternative has been identified in multinucleon transfer (MNT) reactions, which offer a promising route to neutron-rich heavy nuclei. The challenge is to isolate the desired nuclei from the multitude of products generated during the reaction.
We have been working on this reaction mechanism for several years, performing experiments at Argonne National Laboratory and other international laboratories.
The aim of this thesis is to analyse the data collected during the Argonne experiment (end 2023) and to propose a new experiment at the spectrometer Prisma (Legnaro National Lab) coupled with the Agata germanium detector.
Shapes, vibrations and rotations of the 106Cd nucleus studied with gamma-ray spectroscopy with GRIFFIN and AGATA
One of the key questions in the field of nuclear structure concerns the emergence of collectivity, and its link with the microscopic structure of the nucleus. Atomic nuclei can exhibit so-called collective behaviours, which means that their constituents, protons and neutrons, move in a coherent way. The main modes of collective nuclear motion are vibrations and rotations. If a nucleus is not deformed, it cannot undergo rotations when excited, but vibrations around its spherical equilibrium shape are possible.
Even-even isotopes of cadmium have been considered textbook examples of vibrational behaviour. However, this interpretation has been questioned following recent experimental studies, which have, with a guidance from theoretical calculations, led to the reorganization of the level schemes of 110,112Cd in terms of rotational excitations, suggesting the presence of a variety of shapes in these nuclei. Thanks to a recent PhD work in our group, this new interpretation has been extended to the 106Cd nucleus. However, questions remain regarding the nature of certain low-lying excited states in this nucleus. In particular, we obtained indications that some excited states may result from a coupling between the so-called octupole (i.e. the nucleus deforms into a pear shape) and quadrupole (i.e. the nucleus oscillates between elongated and flattened shapes) vibrations. To test this hypothesis, a high-precision beta-decay experiment has been proposed at TRIUMF (Vancouver, Canada) using the world's most advanced spectrometer for beta-decay measurements GRIFFIN, to search for weak decay paths in the 106Cd level scheme, and to unambiguously determine the spins of the excited states through the analysis of gamma-gamma angular correlations. Thanks to this measurement it will be possible to solve multiple puzzles concerning the structure of this nucleus, in particular regarding the possible triaxiality of its ground state and the suspected coexistence of multiple shapes.
The student will be in charge of the analysis of this experiment, which will take place in 2025. Then, based on the results of this analysis, they will proceed to a re-evaluation of the population cross sections of excited levels in 106Cd, which were measured with the new generation gamma-ray spectrometer AGATA at GANIL using the Coulomb excitation technique. From this combination of measurements, we hope to obtain, for the first time in the nuclear chart, the complete set of transition probabilities between the states resulting from the coupling between octupole and quadrupole vibrations. We will then proceed to the interpretation of the results in close collaboration with experts in nuclear-structure theory.
This thesis work will make it possible for the student to follow a research project in its entirety, from the preparation of the experiment to its theoretical interpretation, and to become familiar with several experimental gamma-ray spectroscopy techniques, using the most advanced gamma-ray spectrometers in the world.
Machine-learning methods for the cosmological analysis of weak- gravitational lensing images from the Euclid satellite
Weak gravitational lensing, the distortion of the images of high-redshift galaxies due to foreground matter structures on large scales, is one
of the most promising tools of cosmology to probe the dark sector of the Universe. The statistical analysis of lensing distortions can reveal
the dark-matter distribution on large scales, The European space satellite Euclid will measure cosmological parameters to unprecedented accuracy. To achieve this ambitious goal, a number of sources of systematic errors have to be quanti?ed and understood. One of the main origins of bias is related to the detection of galaxies. There is a strong dependence on local number density and whether the galaxy's light emission overlaps with nearby
objects. If not handled correctly, such ``blended`` galaxies will strongly bias any subsequent measurement of weak-lensing image
distortions.
The goal of this PhD is to quantify and correct weak-lensing detection biases, in particular due to blending. To that end, modern machine-
and deep-learning algorithms, including auto-di?erentiation techniques, will be used. Those techniques allow for a very e?cient estimation
of the sensitivity of biases to galaxy and survey properties without the need to create a vast number of simulations. The student will carry out cosmological parameter inference of Euclid weak-lensing data. Bias corrections developed during this thesis will be included a prior in galaxy shape measurements, or a posterior as nuisance parameters. This will lead to measurements of cosmological parameters with an reliability and robustness required for precision cosmology.