Neutrino Oscillations and Charged Higgs Bosons -Experimental projects for physics beyond the Standard Model

This thesis is based on work done in two different experimental projects. The first project, the Tau RICH, is a previously proposed tau-neutrino appearance experiment for the CERN neutrino beam at the Gran Sasso laboratory in Italy. The proposed experimental concept is based on the use of focusing RICH detectors with liquid radiator (C6F14). Simulations made with a Geant4 code show that in the proposed experimental set-up, Cherenkov light from delta electrons will constitute a severe background that in practice would render the experiment unfeasible. The second project, ATLAS, is a general purpose detector at the CERN 14 TeV proton-proton collider LHC which will start operation in 2007. To make the reconstruction and selection of the events in ATLAS more accurate, complete and up-to-date information on the interaction of the produced particles with the detector is needed. A service program code, the Material Integration Service (MIS), has been developed which makes use of the detector descriptions already available in a Geant4 code and which uses a novel algorithm, based on line integrals evaluated within small volume elements that build up the detector. This code is demonstrated to constitute a practically useful tool of satisfactory performance and accuracy. The charged Higgs boson production in the gluon-bottom quark mode, gb -> tH+, followed by charged Higgs decays into a chargino and a neutralino, is studied for a specific choice of values for the Minimal Supersymmetric Standard Model (MSSM) parameters. It is shown, using a Monte Carlo code to simulate the ATLAS detector and the assumed MSSM physics model, that for an integrated luminosity of 300 fb-1, in the intermediate region 4 < tanβ < 10 where H+ decays to SM particles cannot be used for H+ discovery, charged Higgs decays to non-SM particles can be used for Higgs discovery at the 5 sigma significance level.