Prospects for Charged Higgs Boson Searches at the Large Hadron Collider with Early ATLAS Data

In some theories beyond the Standard Model, such as Supersymmetry, the two complex scalar doublets required for electro-weak symmetry breaking result in, amongst other new particles, two charged Higgs bosons, H ± . This thesis presents the expected sensitivity to the H ± , assuming proton-proton collisions at a centre of mass energy √ s = 10 TeV provided by the Large Hadron Collider and recorded by the ATLAS experiment. At this centre of mass energy, top-quark pairs are produced with a predicted cross section of 401.6 pb, and the H ± are potentially produced in the top quark decay t → bH + , which replaces the Standard Model decay t → bW + . The H ± were assumed to decay to the quark pairs c s or s c , and the presence of the H ± was inferred from a secondary peak in the W -boson mass distribution. A kinematic fitting method was used to gain better separation between the W -boson and H ± mass peaks, and a maximum likelihood method was used to set the expected upper limits on the branching ratio B ( t → bH + ). Assuming 200 pb − 1 of data collected at √ s = 10 TeV, the expected limits range between 4.3% and 17.8%, depending on the H ± mass. This shows that ATLAS should be able to use early data to compete with the Tevatron exper- iments. Since ATLAS is now taking data at √ s = 7 TeV, the expected limits assuming 1 fb − 1 of data with √ s = 7 TeV are also presented. These limits range between 3.5% and 15% depending on the H ± mass.