Abstract: 

Speaker 1: Leonardo Splendori

Title: Developments in b-tagging for the ATLAS upgrade and their impact on di-Higgs sensitivity

Abstract: The upcoming High Luminosity LHC (HL-LHC) era is expected to bring opportunities for studies involving rare processes, including di-Higgs production. Flavour tagging is going to play a crucial role in the analysis of such processes. This talk will explore the challenges we expect to encounter for flavour tagging in the HL-LHC era, with its higher luminosity, increased pile-up and upgraded ATLAS detector. The focus will be on the expected behaviour of current flavour tagging neural networks (GN2) when trained and evaluated on simulated Run 4 samples. To determine its performance and robustness against the harsher conditions associated with higher pileup. From this we will be able to compare the same model between Run 3 and Run 4 and produce predictions on the impact this new environment will have on di-Higgs analyses.

Speaker 2: Mélissa Leroy

Speaker 3: Christian Tsava

Speaker 4: Francesco Magnani

Speaker 1 : Grigorii TOLKACHEV

Title: Search for doubly resonant beyond the Standard Model process with one Higgs boson and one scalar resonance in the final state in the $b\bar{b}\gamma\gamma$ channel in the ATLAS experiment at the LHC.

Abstract: Although the Standard Model (SM) provides an exceptionally accurate description of a wide range of experimental observations, it is nevertheless an incomplete theory. Many theories go beyond the SM (BSM), introducing additional particles and interactions to address its incompleteness. Some BSM models predict the existence of new scalar particles in the Higgs sector, denoted as X and S, which could be produced in proton-proton collisions in association with a Higgs boson: $ pp \rightarrow X \rightarrow SH$. Searches for such particles have been conducted by several analysis teams within the ATLAS and CMS experiments. Notably, one analysis reported a local (global) excess of 3.5$\sigma$ (2.0$\sigma$) for $m_X = 575$ GeV and $m_S = 200$ GeV compared to the background-only hypothesis in the decay channel $X \rightarrow SH \rightarrow b\bar{b}\gamma\gamma$, using 140 fb$^{-1}$ of ATLAS Run 2 data at $\sqrt{s} = 13$ TeV. While this excess is below the discovery threshold of $5\sigma$, it may suggest a possible deviation from Standard Model predictions. This talk will present an update of this search using ATLAS Run 2 data at $\sqrt{s} = 13$ TeV and part of Run 3 data at $\sqrt{s} = 13.6$ TeV (2022-2023). The new search follows a similar strategy to the Run 2 analysis, with several improvements.

Speaker 2: Diane JOLY

Title: Measuring neutrino oscillations with KM3NeT/ORCA

Abstract: KM3NeT is a next-generation neutrino observatory being constructed in the Mediterranean Sea. It consists of two main detector configurations: ORCA, optimized for low-energy (GeV) neutrinos and mass-hierarchy studies, and ARCA, designed for high-energy (TeV) cosmic neutrinos for astrophysical purposes. Currently, the ORCA detector has 33 detection lines deployed, with 18 optical modules on each line, with plans to eventually reach a full configuration of 115 lines. In the first physics analyses performed with the partially completed ORCA, the results are already competitive with current measurements, demonstrating strong sensitivity to neutrino oscillation parameters. However, these measurements remain limited by several sources of systematic uncertainty, particularly in modeling the detector response. The objective of my PhD thesis is to improve the estimation of these systematic uncertainties, taking into account the quantum efficiency of the optical modules, and the water absorption length. By developing more accurate models of the detector response, I aim to reduce the dominant systematic errors and enhance the precision of future ORCA analyses.

Speaker 3: Isaac-Paul CONSIGNY

Title: Search for lepton flavor violating decay B0 → ρ0τ ℓ at Belle II

Abstract: Lepton flavour conservation is an accidental symmetry of the Standard Model (SM).  
However, the discovery of neutrino oscillations has already demonstrated that this symmetry is not exact,
implying that lepton flavour can be violated in nature.
Many extensions of the SM naturally predict additional sources of lepton flavour violation (LFV) with enhanced branching fractions for processes involving the third generation of leptons, making searches for such effects an important probe for new physics. Searches for related processes such as b → sτ ℓ had been extensively studied at Belle II but b → dτ ℓ remains uncovered. This work presents the first investigation of lepton flavour violation in B → ρ0τ ℓ decay modes, using the combined datasets of Belle and Belle II experiments.

Talk 1 - Ching-Hua Li: Test tau - e universality at LHCb

Abstract: The SM includes three lepton families: electrons, muons, and tau leptons, each associated with a corresponding neutrino type. A key feature of the SM is the universality of the electroweak gauge coupling among the three known fermion families, known as lepton flavor universality (called LFU). Any significant observation of a deviation from this universality, occurring in SM only when the phase space or amplitude becomes dependent on lepton mass, would indicate new physics beyond the SM. The test of LFU is aimed at measuring such deviations in the extent of lepton flavor symmetry breaking relative to SM predictions. This talk will present my study using the branching fraction ratio between the semileptonic decays B -> D* e nu and B -> D* tau nu with tau -> e nu nu, to test LFU in LHCb.

Talk 2 - Sarah Ferraiuolo : Probing Cosmology with Gravitational-Wave and Euclid data

Talk 3 - Raphael BERTRAND: Optimisation of embedded neural networks for the energy reconstruction of the liquid argon calorimeter cells of ATLAS

Abstract: The Large Hadron Collider (LHC) collides protons at nearly the speed of light, producing new particles observed by the ATLAS detector. In 2026, the LHC will undergo a major upgrade to the High-Luminosity LHC (HL-LHC), increasing luminosity by a factor of 5–7 and delivering up to 200 simultaneous collisions. To cope with the resulting data rates, ATLAS will replace the readout electronics of the Liquid Argon Calorimeter (LAr) as part of its Phase-II upgrade. The new LASP board, equipped with two FPGAs, will perform real-time energy reconstruction for 384 channels each, covering about 180,000 calorimeter cells in total.
At high pileup, overlapping electronic pulses challenge the current Optimal Filtering (OF) algorithm used to compute the energy. Neural network (NN)–based alternatives are being explored to surpass OF while respecting FPGA constraints: <125 ns latency and limited resource usage. After earlier studies of recurrent and convolutional architectures, a dense-layer design is proposed, reducing both latency and resource consumption.
Bayesian hyperparameter optimisation is used to adapt the network size, balancing energy resolution with FPGA feasibility. The results show how to achieve optimal performance within hardware limits. In addition, deep evidential regression is employed to estimate uncertainties by fitting predicted energies to probability distributions, enabling quantification of both data noise and model imprecision with minimal overhead.
The talk will compare network architectures and present the Bayesian optimization results, as well as demonstrate uncertainty estimation with evidential regression

Abstract: The observation of the Higgs boson by the ATLAS and CMS collaborations at CERN in 2012 is without a doubt one of the most significant milestones in the history of particle physics. It confirmed our understanding of the origin of particle masses, and proved the theoretical soundness of the Standard Model of particle physics. This discovery happened more than 13 years ago; is the Higgs boson now "old news"? Not at all! In this seminar, I will explain why the Higgs boson's relationship with fermions is fundamental to our understanding of nature and how studying its interactions with charm and beauty quarks can shed light on the flavor puzzle of the Standard Model. I will also go over exciting recent, ongoing, and future experimental developments at the LHC and beyond.

Zoom: https://univ-amu-fr.zoom.us/j/96864416838?pwd=K8T5LWaJXROnA0R0SpmjRRiHLure4m.1

Résumé: Que ce soit à la surface de la Terre ou dans ses profondeurs, dans les abysses océaniques ou dans l’atmosphère, la radioactivité est présente partout et la vie aussi. Quel rôle a pu jouer la radioactivité naturelle dans l’émergence et l’évolution de cette vie depuis plusieurs milliards d’années ? Explorer cette question requiert de caractériser et de comprendre la radioactivité des différents compartiments du système Terre (atmosphère, océan, surfaces continentales, terre solide).  A travers quelques activités de recherche pluridisciplinaires sur les volcans actifs, les sources minérales et en laboratoire souterrain ou plus récemment sur l’atmosphère et les fonds océaniques, nous illustrerons combien la radioactivité naturelle demeure encore mal connue ainsi que son impact sur le vivant. Ces exemples illustreront toute la richesse et le potentiel des interactions entre biologie, géosciences et physique nucléaire.