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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.
