In this dissertation, I present a search for non-standard decays of a Standard Model-like Higgs boson to pairs of light bosons, as predicted in models with extended Higgs sectors. In two Higgs ...doublet models, including the next-to-minimal supersymmetric standard model, the Higgs boson can decay into a pair of light pseudoscalars a. In this search, the gluon fusion, W and Z associated Higgs, and vector boson fusion production channels for the Higgs are all considered, and the decay H → aa with a → ττ is reconstructed from the tau decay products. The final state is characterized by one isolated high p T muon plus at least one highly boosted pair of taus, of which one of the taus is required to decay to a muon. Using 19.7 fb–1 of 8 TeV center of mass pp collision data recorded by the Compact Muon Solenoid experiment at the Large Hadron Collider, a counting experiment is performed in a region of high di-tau invariant mass. We have found no excess of events above the Standard Model backgrounds, and the observed data is used to set upper limits on the branching ratio Br(H → aa)Br 2(a → ττ). These results are equally applicable to decays of the SM-like Higgs boson to a pair of light scalars h.
Results on the effects of ionizing radiation on the signal produced by plastic scintillating rods manufactured by Eljen Technology company are presented for various matrix materials, dopant ...concentrations, fluors (EJ-200 and EJ-260), anti-oxidant concentrations, scintillator thickness, doses, and dose rates. The light output before and after irradiation is measured using an alpha source and a photomultiplier tube, and the light transmission by a spectrophotometer. Assuming an exponential decrease in the light output with dose, the change in light output is quantified using the exponential dose constant \(D\). The \(D\) values are similar for primary and secondary doping concentrations of 1 and 2 times, and for antioxidant concentrations of 0, 1, and 2 times, the default manufacturer's concentration. The \(D\) value depends approximately linearly on the logarithm of the dose rate for dose rates between 2.2 Gy/hr and 70 Gy/hr for all materials. For EJ-200 polyvinyltoluene-based (PVT) scintillator, the dose constant is approximately linear in the logarithm of the dose rate up to 3400 Gy/hr, while for polystyrene-based (PS) scintillator or for both materials with EJ-260 fluors, it remains constant or decreases (depending on doping concentration) above about 100 Gy/hr. The results from rods of varying thickness and from the different fluors suggest damage to the initial light output is a larger effect than color center formation for scintillator thickness \(\leq1\) cm. For the blue scintillator (EJ-200), the transmission measurements indicate damage to the fluors. We also find that while PVT is more resistant to radiation damage than PS at dose rates higher than about 100 Gy/hr for EJ-200 fluors, they show similar damage at lower dose rates and for EJ-260 fluors.
