UC Santa Barbara

This thesis presents a measurement of the cross section for the production of two W bosons and one Z boson. The measurement is performed using data collected by the CMS experiment at the CERN LHC at center-of-mass energies √s = 13 and 13.6 TeV, corresponding to an integrated luminosity of 200 fb−1. Events with four charged leptons (electrons or muons) are selected for this analysis. Both nonresonant W W Z production and ZH production, with the Higgs boson decaying into two W bosons, are reported. For the first time, the two processes are measured separately in a simultaneous fit. Combining the two modes, signal strengths relative to the standard model (SM) predictions of 0.75+0.34 −0.29 and 1.74+0.71 −0.60 are measured for √s = 13 and 13.6 TeV, respectively. The observed (expected) significance for the triboson signal is 3.8 (2.5) standard deviations for √s = 13.6 TeV, thus providing the first evidence for triboson production at this center-of-mass energy. Combining the two modes and the two center-of-mass energies, the inclusive signal strength relative to the SM prediction is measured to be 1.03+0.31 −0.28, with an observed (expected) significance of 4.5 (5.0) standard deviations. The focusing of collider beams for collider experiments is crucial for maximizing the luminosity and thus the discovery potential of these machines. In recent years, plasma wakefield acceleration has emerged as a leading candidate for achieving higher energy collisions with smaller facility footprints due to the large accelerating gradients in the plasma. This higher beam energy poses significant challenges for the final focusing system of the collider. Here, we discuss the various challenges of final focusing for TeV-scale plasma accelerators and propose possible solutions. Finally, we present the first design of a final focusing system for a 10 TeV linear wakefield collider, evaluate its performance, and discuss its shortcomings as well as improvements for future designs.