Particle Collider Probes of Dark Energy, Dark Matter and Generic Beyond Standard Model Signatures in Events With an Energetic Jet and Large Missing Transverse Momentum Using the ATLAS Detector at the LHC

Various Beyond Standard Model signatures are probed using a monojet analysis with the ATLAS experiment using $\sqrt{s} = $ 13 TeV proton-proton collision data, and model-independent limits on generic Beyond Standard Model signatures are set. Three specific Beyond Standard Model signatures are highlighted: Horndeski dark energy and axial-vector and pseudoscalar WIMP candidates. Limits are reported at 95$\%$ confidence level observed(expected). For the WIMP candidates limits extend to $m_{Z_{A}} \geq $ 2060(2175) GeV and $m_{Z_{P}} \geq $ 368(404) GeV for the dark matter mass of axial-vector and psedudoscalar cases respectively, with a mediator mass of 1 GeV. This extends the reach of the axial-vector WIMP limits by 500(400) GeV from previous monojet searches, while this is the first time this channel in ATLAS is sensitive to the pseudoscalar WIMP. For the Horndeski dark energy model, limits are set at a cross section of $\sigma \leq $ 0.0433(0.0366) fb and mass scale of $M_{2} \geq $ 1558(1591) GeV, an improvement of 400(300) GeV over using only the 2015+2016 data, which is the first time a dark energy model has been probed in a particle collider based search. Numerous improvements were made to the previous monojet analysis to perform these measurements and increase the model independent reach. In addition this thesis presents preliminary results in developing a realtime beam monitor for the Birmingham MC40 cyclotron, the aim being to allow more precise irradiations of components which will be used in the High Luminosity-LHC upgrade. This precise irradiation will enable measurements of their radiation hardness, a vital property of components which will need to survive the high radiation levels near the interaction points in the High Luminosity-LHC.