Searches for Supersymmetry with compressed mass spectra using monojet events with the CMS detector at the LHC

A novel search for supersymmetric particles in events with one high transverse momentum jet and large missing transverse energy is performed using an integrated luminosity of 19.7 fb$^{-1}$ of pp collision data collected using the CMS detector at the Large Hadron Collider. By using events with an energetic radiated jet, sensitivity to supersymmetric models with compressed mass spectra is gained where the decay products have very low energy. Standard Model background estimates are evaluated with the use of data control samples. No excess over Standard Model expectations is observed, and limits are placed on third generation squark production at the 95% confidence level using supersymmetric simplified models. The development of a Level 1 trigger algorithm to reconstruct jets in the Phase 1 Upgrade of the CMS detector is presented. Utilising the full granularity of the CMS calorimeter and time-multiplexed-trigger technology, a new algorithm with increased flexibility and resolution is presented. It is possible to measure and subtract the contribution to calorimeter deposits of soft particles originating from multiple pp vertices in an event, on an event-by-event basis, in order to decrease the trigger rates associated with high luminosity future run conditions. This will enable CMS to maintain, or better, its ability to do physics as centre-of-mass energy and instantaneous luminosity of the LHC increases in the years to come.