UC Riverside

This dissertation presents a search for the Standard Model production of four top quarks (pp$\rightarrow$\tttt) using events with opposite-sign dilepton ($\mu^+\mu^-$, $\mu^\pm e^\mp$, or $e^+e^-$)+jets signatures. The data used in this analysis are from proton-proton collisions at a center-of-mass energy $\sqrt{s}=13$ TeV recorded by the CMS detector at LHC during year 2016. The total integrated luminosity of the data corresponds to 35.8 $\mathrm{fb}^{-1}$. A multivariate analysis method is used to discriminate \tttt signal events from background events based on global event and jet properties. No significant deviation is observed in data from the prediction of the background. An upper limit is set on the cross section of Standard Model \tttt production to be 64 fb at 95\% confidence level. A combination of the measurements with results from single-lepton ($\mu$, $e$)+jets final states and a previous measurement from the CMS experiment is performed and the combined cross section measurement is $13^{+11}_{-9}$ fb, with an observed signal significance of 1.4 standard deviations.