Single-top s-channel cross-section measurement and sensitivity to a charged Higgs boson

At the LHC, top quarks are mainly produced via the pair production mechanisms. Although non-dominant, the single-top production is however far from being negligible with a total cross-section of about a third of that the pair production. If a 5 sigma-evidence of single-top events at the Fermilab p\bar{p} collider is likely to occur by the end of the Run II, precise measurements will only be possible at the LHC. They should allow the determination of all three separate contributions to the total single-top cross-section, thus providing valuable tests of the electro-weak top production. This report focusses on the determination of the s-channel contribution to the single-top cross-section. Although this contribution accounts for only 1/30 of the single-top production, this measurement constitutes a powerfull probe for new physics, this channel being directly sensitive to the presence of an extra charged boson. In a first Section, the phenomenology of the single-top at the LHC is presented. In the following part, the selection developped to discriminate the signal from backgrounds is outlined and its performance in terms of statistical sensitivity and systematic uncertainties are detailed. In the last part of the document, the sensitivity to a charged higgs boson predicted in two Higgs Doublet Models, has been assessed in the (m_H,tan(beta))plane. Results show that this measurement could be one of the main components in charged Higgs boson searches.