Particle Physics Division

The Higgs boson, discovered in 2012 at the LHC, is at the origin of the electroweak symmetry breaking within the Standard Model (SM). Despite extensive studies on the Higgs properties, the Higgs self-coupling remains unexplored. This parameter is a key factor in determining the Higgs potential and the stability of the universe’s vacuum. Studying Higgs pair production is the only direct method for measuring this self-coupling, which will give crucial insights into the universe’s fundamental structure and the nature of the electroweak phase transition after the Big Bang. Di-Higgs production is predicted to have a very small cross-section within the SM. Among possible detection channels, the multilepton final state is promising due to its unique kinematic signature, though challenging due the need for precise lepton identification and advanced signal separation techniques using machine learning. This PhD project focuses on searching for di-Higgs production in the multilepton channel with 13.6 TeV ATLAS data, taking advantages from the increased data and energy in Run 3 and aiming to approach SM sensitivity.

The goal of this PhD project is to develop a novel joint analysis for the DESI galaxy clustering
and Planck PR4/ACT CMB lensing data, based on numerical simulations of the surveys and
state-of-the-art machine learning and statistical inference techniques. The aim is to overcome
many of the limitations of the traditional approaches and improve the recovery of cosmological
parameters. The joint galaxy clustering - CMB lensing inference will significantly improve
constraints on the growth of structure upon DESI-only analyses and refine even more the test of general relativity.

Galaxy clusters, located at the node of the cosmic web, are the largest gravitationally bound structures in the Universe. Their abundance and spatial distribution are very sensitive to cosmological parameters, such the matter density in the Universe. Galaxy clusters thus constitute a powerful cosmological probe. They have proven to be an efficient probe in the last years (Planck, South Pole Telescope, XXL, etc.) and they are expected to make great progress in the coming years (Euclid, Vera Rubin Observatory, Simons Observatory, CMB- S4, etc.).
The cosmological power of galaxy clusters increases with the size of the redshift (z) range covered by the catalogue. Planck detected the most massive clusters in the Universe in the redshift range 0 Only the experiments studying the cosmic microwave background will be able to observe the hot gas in these first clusters at 2 One thus needs to understand and model the emission of the gas as a function of redshift, but also the emission of radio and infrared galaxies inside the clusters to be ready to detect the first clusters in the Universe. Irfu/DPhP developed the first tools for detecting clusters of galaxies in cosmic microwave background data in the 2000s. These tools have been used successfully on Planck data and on ground-based data, such as the data from the SPT experiment. They are efficient at detecting clusters of galaxies whose emission is dominated by the gas, but their performance is unknown when the emission from radio and infrared galaxies is significant.
This thesis will first study and model the radio and infrared emission from galaxies in the clusters detected in the cosmic microwave background data (Planck, SPT and ACT) as a function of redshift.
Secondly, one will quantify the impact of these emissions on existing cluster detection tools, in the redshift range currently being probed (0 Finally, based on our knowledge of these radio and infrared emissions from galaxies in clusters, we will develop a new cluster extraction tool for high redshift clusters (2 The PhD student will join the Simons Observatory and CMB-S4 collaborations.

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.

Positron emission tomography (PET) is a nuclear medical imaging technique widely used in oncology and neurobiology.
We're proposing you to contribute to the development of an ambitious, patented technology: ClearMind. This gamma photon detector uses a monolithic PbWO4 crystal, in which Cherenkov and scintillation photons are produced. These optical photons are converted into electrons by a photoelectric layer and multiplied in a MicroChannel plate. The induced electrical signals are amplified by gigahertz amplifiers and digitized by SAMPIC fast acquisition modules. The opposite side of the crystal will be fitted with a matrix of silicon photomultiplier (SiPM).

You will work in an advanced instrumentation laboratory in a particle physics environment .
The first step will be to optimize the "components" of ClearMind detectors, in order to achieve nominal performance. We'll be working on scintillating crystals, optical interfaces, photoelectric layers and associated fast photodetectors, and readout electronics.
We will then characterize the performance of the prototype detectors on our measurement benches.
The data acquired will be interpreted using in-house analysis software written in C++ and/or Python.
Finally, we will compare the physical behavior of our detectors to Monté-Carlo simulation software (Geant4/Gate).
A particular effort will be devoted to the development of ultra-fast scintillating crystals in the context of a European collaboration.

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.

The proposed thesis project focuses on studying neutrino oscillations, a key quantum phenomenon for exploring New Physics beyond the Standard Model. These oscillations, compared between neutrinos and antineutrinos, could shed light on one of the most fundamental questions in particle physics: the origin of the matter-antimatter asymmetry in the Universe.

The T2K experiment, located in Japan, studies these oscillations by generating an intense beam of muon neutrinos (and antineutrinos). This beam is measured at two points: a near detector, used to reduce systematic uncertainties related to the neutrino flux and interaction models, and a far detector (Super-Kamiokande), responsible for measuring the disappearance of muon neutrinos and the appearance of electron neutrinos after oscillations.

The thesis project is divided into two parts. The first part will involve calibrating the new detectors (new time projection chambers using resistive MicroMegas technology) to measure the neutrino energy spectrum and assess the associated systematic uncertainties. The second part will focus on analyzing the newly collected data, allowing for more precise measurements of oscillation parameters, improving the understanding of neutrino-nucleus interactions, and measuring CP violation in neutrino oscillations with 3 sigma significance in the case of maximal violation, as indicated by the latest T2K results, and ultimately 5 sigma in the future Hyper-Kamiokande experiment, which will use the same beam and near detector as T2K.

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.

Neutrinos are promising messengers for detecting physics beyond the Standard Model. Their elusive nature and unexplained mass suggest they could open new pathways for physics. Neutrino oscillation research has entered a precision era with experiments like T2K, which in 2020 observed hints of CP violation in the leptonic sector that could shed light on the question of matter-antimatter asymmetry in the Universe.

The T2K experiment, located in Japan, studies neutrino oscillations by generating an intense beam of muon neutrinos (and anti-neutrinos). This beam is measured at two locations: a near detector, designed to reduce systematic uncertainties related to the neutrino flux and interaction models, and a far detector (Super-Kamiokande), tasked with measuring the disappearance of muon neutrinos and the appearance of electron neutrinos after oscillation.
In 2023, T2K entered its second phase with increased beam power and upgrade of the near detector, including a highly granular new target and High-Angle Time Projection Chambers (HA-TPC). These improvements enable more precise reconstruction of particles produced by neutrino interactions.

IRFU teams contributed by developing HA-TPCs equipped with resistive Micromegas technology. This work improves spatial resolution and the precision of particle momentum. The thesis explores optimizing the particle track reconstruction algorithms in the HA-TPCs using advanced techniques, as well as analyzing T2K data with the upgraded ND280 to achieve a 3 sigma level of significance for CP violation. T2K is thus paving the way for future experiments like DUNE and Hyper-Kamiokande, opening new perspectives for the next two decades.