Search for New Physics Processes with Heavy Quark Signatures in the ATLAS Experiment

A program involving searches for new physics with heavy quark final states using data from the ATLAS experiment at the LHC is presented here. The signal and expected backgrounds for the decay $B_{s}→μ^{+} μ^{-} μ^{+} μ^{-}$, a rare decay whose branching ratio may be enhanced by the presence of certain Beyond the Standard Model processes, are studied, and the groundwork is laid for a future analysis. Possible mediators include horizontal gauge bosons, supersymmetry via sgoldstinos, and interactions with the hidden sector. To this end, a set of twelve triggers have been selected and studied, and their efficiency figures of merit have been calculated. A truth trigger efficiency study was performed in order to determine if new triggers should be installed for the analysis. The backgrounds have been studied, and a mass window technique was used to reduce their amplitude relative to the signal. A proposal to improve the efficiency of some of the ATLAS High-Level B-physics Triggers, based on refining the selection criteria for the quality of the fit for $J⁄ψ→μ^{+} μ^{-}$ vertices, was developed. A new $J⁄ψ$ vertex fit $χ^{2}$ selection criterion was developed using Run-1 triggers, reducing the original $χ^{2}<20$ criterion to $χ^{2}<10$. This was installed for Run-2 data-taking. A similar study was performed on Run-2 data, and signal efficiency, background rejection, and Receiver Operating Characteristic plots were generated for these data. Instrumentation for future ATLAS runs has been developed as well, including software for a diode array used to measure charged particle beam fluence in real time. Noise reduction studies of a device for studying charge collection in irradiated particle sensors was performed, and it was determined that the noise might be decreased by an additional electronic noise filter.