The vapor pressure isotopic effect (VPIE) of xenon has been measured using cryogenic distillation. The still is calibrated with argon and krypton and yields a measurement of ln­(p 130/p 136) ≃ (0.26 ± 0.04) × 10–3, where p 130 and p 136 are the vapor pressures of 130Xe and 136Xe at the nominal boiling point, respectively. The dependence of the VPIE across the isotopes for the three elements is found to be approximately linear with atomic mass, and all values are consistent with theoretical expectations.

Analysis work is presented as part of an ongoing search for Emerging Jet (EJ) signals within the ATLAS detector at the Large Hadron Collider. These EJ signals arise in models with a hidden valley, QCD-like dark sector, which is linked to the Standard Model (SM) sector via a dark mediator particle, X d , with a mass on the order of a TeV. These X d particles are pair-produced during proton-proton collisions and each quickly decays into a SM quark and a dark quark. These dark quarks hadronize into long-lived dark hadrons. Dark pions are of primary interest and decay back into SM particles with a mean decay length ranging between cτ πd = 0.5mm and 300mm, causing a jet to emerge within the detector. These EJs are characterized by their high p T and multiple displaced vertices. The analysis uses Monte Carlo events simulated with a hidden valley implementation of PYTHIA (version 8.230) scaled to the LHC Run 2 data period (2015 -2018) with integrated luminosity of 139f b −1 and √ s = 13 TeV. This thesis includes a comparison study between these emerging jets and typical QCD jets, and a trigger study to verify that the trigger used for the analysis is efficient in the search region of interest. Finally, a sensitivity study to probe the theoretical crosssections of the EJ signal models is presented, which utilizes a data-driven ABCD method for two model-independent planes and a more complex, machine-learning, model-dependent plane.I would like to thank my supervisor, Jesse Heilman, for your guidance and excellent explanations of physics and ATLAS related topics, which always left me inspired to learn more. A huge thanks to Kevin Graham and Mohsen Naseri as well, for your many hours of guidance, insight, and feedback.Additional thanks to my fellow student colleagues Ian Ramirez-Berend and JérémieLePage-Bourbonnais for all of your help. And a special thanks to the entire Emerging Jets ATLAS analysis team.Thank you also to Daniel Stolarski for your time and feedback during my defence, as well as the great lectures throughout my undergrad and graduate studies.Thank you to my friends that pushed me to go back to school and pursue my interest in physics. You helped me greatly improve my life.Finally, thank you to my parents for all your love and support throughout my whole life and for giving me every opportunity to succeed.

A central topic in the development of understanding of the nature of neutrinos is the search for neutrino-less double beta decay. As increasingly sensitive detectors are required for such searches, a major cost and feasibility concern is the availability of sufficient separated isotope for the chosen target. 136Xe is a very attractive target for these studies. At present this isotope is only available from the Centrifuge systems in Russia. We are exploring the feasibility of doing this enrichment using distillation. To start this study we require the vapour pressure differences of the xenon isotopes which have not been measured to date. This paper will describe the measurement of these vapour pressures using a tall cryogenic distillation process.