UC Santa Barbara

The second run of $pp$ collisions at the Large Hadron Collider (LHC) at CERN marks one of the most anticipated eras in the field of particle physics. Already the largest and most powerful science experiment of its kind, the LHC has outdone itself, running at a record center of mass energy of $\sqrt{s}=13$ TeV and colliding protons at rates of over 600 million collisions per second. The incredible performance of the machine allows for unprecedented exploration of the TeV scale. No elementary particles have ever been observed at these energies, yet many are hypothesized as extensions to the standard model (SM), the most complete and widely accepted model of elementary particles and their interactions. Among the most sought-after hypothetical particles are those proposed by the theory of supersymmetry (SUSY).

In this thesis, results are presented from a generic search for strongly produced

supersymmetric particles in $pp$ collisions in the multijet + missing

transverse momentum final state. The largest analyzed data sample corresponds to 35.9

fb$^{-1}$ recorded by the CMS experiment at $\sqrt{s}=13$ TeV in 2016. This search

is motivated by SUSY models that avoid

fine-tuning of the Higgs mass. In such models, strongly produced SUSY particles,

including the gluino and top squark, are predicted to have masses on

the order of a TeV. These particles also have some of the highest

production cross sections in SUSY and give rise to final states with

distinct, high jet multiplicity event signatures. To make the analysis

sensitive to a wide range of such final states, events are classified

by the number of jets, the scalar sum of the transverse momenta of the

jets, the vector sum of the transverse momenta of the jets, and the

number of b-tagged jets.

All SM backgrounds are measured using dedicated control samples in data. No significant

excess is observed beyond the measured SM expectation. The results are

interpreted as limits on simplified SUSY models. In these models,

gluinos with masses as high as 1970 GeV and squarks with masses as high as 1450 GeV are excluded at 95\% CL for

scenarios with low $\tilde{\chi}_{1}^{0}$ mass, far exceeding the limits

set in Run I.