Construction and Testing of Large-Area GEM Detectors for the Forward Muon Endcap Upgrade of the CMS Experiment and Vector-Portal Search for Dark Matter Particles with Dimuon Pairs at √s = 13 TeV

Abstract

In this thesis, I present my contributions to the second major upgrade of the Compact Muon Solenoid at the Large Hadron Collider and the analysis that I performed on the data collected by the Compact Muon Solenoid during the 2018 and 2017 era. Alongside my team, I assembled and tested ten Gaseous Electron Multipliers to upgrade the forward region at the Compact Muon Solenoid, all of which are now installed at the dedicated stations. The campaign for producing these detectors succeeded in a twoyear-long prototyping endeavor, where I examined the procedural steps for production to optimize the production and testing procedural eciency. I dedicate the more extensive portion of this dissertation to the analysis of the dataset, corresponding to 59.7 fb1 of proton-proton collisions at ps = 13 TeV recorded during 2018, wherein I interpret the model-independent results of the analysis in the context of a dark matter model, by setting 95% upper exclusion limits on the parameters of the model. The model involves a vector-portal i.e., a dark Z boson (ZD), and its decay to dark scalars (sD) which subsequently decay to a four muon final state (pp ! ZD ! sDsD ! 4µ). While I conclude the 2018 analysis by declaring no significant deviation from the predicted background, to improve the background modeling and better statistics, I discuss the progress in analyzing the 2017 era dataset to be combined with the 2018 results.