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Study of the ElectroWeak Symmetry Breaking and the Higgs Sector with the ATLAS detector at the LHC (EWSB)
Date du début: 1 avr. 2013, Date de fin: 31 mars 2017 PROJET  TERMINÉ 

"The Standard Model (SM) of particle physics is the most successful physical theory to date. Its main phenomenology has been confirmed, and it has withstood quantitative test of unprecedented precision in various facilities for 30 years now. Its only piece lacking direct experimental observation is the mechanism of electroweak symmetry breaking, providing with mass the weak gauge bosons and it is related to the appearance of the SM Higgs boson. Following the observation of a new particle by ATLAS and CMS experiments at the CERN Large Hadron Collider (LHC) in summer 2012, the SM is possibly completed.With the current experimental precision, the new particle production and decay patterns are compatible with those of the SM Higgs boson. To unambiguously characterize this new particle, detailed studies of its properties (mass, production rates, spin/CP quantum numbers, self-couplings) are needed, while searches for other similar particles are important. Deviations from the SM expectations or new particles, would be direct observation of new physics phenomena. These studies are currently the highest priority items in the particle physics agenda.The proposed research will use the experience on the searches in the H->ZZ(*)->4l final state, to provide answers to these questions. This final state, although it has low event rates, is ideal for such studies because it is fully reconstructed with high precision and offers the best signal-to-background ratio in the LHC. By 2017, it will provide the best single channel mass measurement. The measurement of production rates at exclusive final states, enhancing specific production mechanisms (vector-boson fusion, associated production with a vector boson), will be invaluable for the study of the couplings. For spin/CP, it will dominate the sensitivity for a graviton-like resonance and will put stringent limits on potential CP-violating components. Finally, it will dominate the searches for additional similar heavy particles."