Search for the Standard Model Higgs boson in H-> tau tau decays with ATLAS detector

• Dimitri Varouchas

Room: salle 9 In this seminar, a search for the Standard Model (SM) Higgs boson decaying into a pair of tau leptons will be reported. The analysis is based on data samples of p-p collisions collected by the ATLAS experiment at the LHC and corresponding to integrated luminosities of 4.6 ifb and 13.0 ifb at centre-of-mass energies of sqrt(s)=7 TeV and 8 TeV, respectively. The observed (expected) upper limit at 95% CL on the cross-section times the branching ratio for SM H→τ+τ− is found to be 1.9 (1.2) times the SM prediction for a Higgs boson with mass mH=125~GeV. For this mass, the observed (expected) deviation from the background-only hypothesis corresponds to a local significance of 1.1 (1.7) standard deviations.

The understanding of the Electroweak Symmetry Breaking after the discovery of a Higgs-like boson with the ATLAS detector

• Andrea Coccaro

Room: salle 9 A new era of precise measurements in particle physics undoubtedly began with the discovery of the Higgs-like particle announced by both the ATLAS and CMS collaborations on July 4th, 2012. The new discovered particle resembles in many ways the Higgs boson responsible of the Electroweak Symmetry Breaking (EWSB) in the Standard Model (SM) even if its discovery was only driven by the most sensitive channels for the low-mass region, H->gammagamma and H->ZZ->4l. Precise measurements of all the possible couplings with both SM and exotics particles and the determination of the mass, spin and parity represent the natural next steps ahead for the LHC community to deeply understand the EWSB in elementary particle physics. In this seminar, I will present my present and future involvement in probing the nature of the EWSB mechanism studying the H->bb decay mode to verify its couplings to fermions and studying an invisibly decaying Higgs boson with a branching ratio down to ~10% to explore possible new physics contributions beyond the SM. Different but complementary aspects of this project are all considered, e.g. the triggering strategies, the reconstruction techniques, the calibration of the b-tagging algorithms and the analysis techniques, since my interests spans in all these different activities.