Search for supersymmetry in channels with two Higgs bosons and missing transverse momentum at CMS

We present a search for physics beyond the Standard Model in channels with two Higgs bosons, each decaying via the process H$\rightarrow$bb, and large missing transverse momentum. The search uses a data sample produced in proton-proton collisions with center-of-mass energy $\sqrt{s}$ = 13 TeV, collected by the CMS experiment at the CERN LHC, and corresponding to an integrated luminosity of 137 fb$^{-1}$. The Standard Model backgrounds are predicted using data-driven techniques and the prediction is compared to the signal region yields to test for the presence of new physics. The observed yields in the signal regions agree with the background estimation, enabling us to set limits on the production cross sections for pairs of the lightest neutralino $\chi_{1}^{0}$ and pairs of gluinos using simplified supersymmetry models. For the electroweak production of nearly degenerate higgsinos, $\, \chi_{1}^{0}$ masses in the range 175 to 1025 GeV are excluded. Gluinos as heavy as 2330 GeV are excluded. These represent the best limits to date for these simplified models, significantly extending the exclusions from previous results. This search is also used in tandem with five other analyses in an electroweakino combined search, extending the limits further than any individual analysis. In addition to these searches, this thesis describes the on-going and future upgrades to the LHC and the CMS detector and experiment. The upgrades are designed to substantially increase the instantaneous luminosity of the LHC, making it easier for future analyses to probe new physics.