Search for dark matter in the mono-jet events at the CMS experiment and detector R&D for the dune experiment

This thesis consists of two studies. The first study aims to search for evidence of a Dark Higgs boson in the mono-Hs final state using the entire dataset of 137.2 fb 􀀀1 collected by CMS during Run 2 using proton-proton collisions with a center-of-mass energy of 13 TeV. We employ variables such as pmiss T and the mass of the recoiling large-cone jet to identify a possible mono-Hs signature. However, the analysis is model-dependent, and the pmiss T distribution and mass spectrum of the large-cone jet require a detailed analysis to be generalized. The second study discusses the performance of Xenon doping in the liquid argon environment at ProtoDUNE-SP. The study aims to recover light losses due to nitrogen contamination and maintain the purity of argon in time projection chamber experiments. We demonstrate the effects of injecting Xenon into liquid argon on the detector's performance and compare them to the initial results. The study presents a comprehensive analysis of the performance of the first Xenon doping at ProtoDUNE-SP. These studies demonstrate the ongoing efforts in the search for new physics and the advancements in detector technology.