Search for Higgs bosons beyond the Standard Model in early ATLAS data

Higgs bosons are present in many extensions of the Standard Model, yet we are still waiting for the experimental confirmation of their existence. This thesis discusses Minimal and Next-to Minimal Supersymmetric Models, and presents searches for leptonic Higgs boson decays in channels that may provide the first unambiguous evidence of Higgs physics beyond the Standard Model. The channels considered are : gg→a1, gg→h1→2a1, H+→τν, and H+→a1W+, where a1→µµ and τ→ℓνν. A full data analysis is presented for gg→a1→µµ channel, while sensitivity prospects are discussed for the other channels. For the data analysis, we consider a data set with an integrated luminosity of 39 pb−1 collected by the ATLAS Detector at the Large Hadron Collider in 2010, operating at the centre of mass energy of √s = 7 TeV. As we observe no evidence for a signal in the gg→a1 channel, we set a model independent 95% confidence level upper limit on Higgs production cross section and branching ratio: σgg→a1×B(a1→µµ). This result represents the first measurement of σgg→a1×B(a1→µµ) in the world, and improves on the current experimental constraints on the Higgs sector beyond the Standard Model.