An inclusive search for new physics in events with fully hadronic final states using the MT2 variable is presented. The results are based on a sample of 13 TeV center-of-mass energy proton-proton collisions, corresponding to 2.3 fb-1 of integrated luminosity collected with the CMS detector at the LHC in 2015. No excess event yield above the Standard Model background expectation is observed. The results are interpreted as limits on simplified models of supersymmetry, expressed as limits on the masses of potential new colored particles. Assuming a stable LSP with mass less than 500 GeV, gluino masses up to 1550-1750 are excluded at 95% confidence level, depending on the gluino decay mechanism. For models of direct squark pair production, top squarks with masses up to 800 GeV are excluded. Bottom squarks with masses up to 880 GeV are excluded. Light flavor squarks with masses up to 600-1260 GeV, depending on the degeneracy of squark masses, are excluded.

A search for new physics is performed using events that contain one or more jets, no isolated leptons, and a large transverse momentum imbalance, as measured through the MT2 variable, which is an extension of the transverse mass in events with two invisible particles. The results are based on a sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, and that corresponds to an integrated luminosity of 2.3 inverse femtobarns. The observed event yields in the data are consistent with predictions for the standard model backgrounds. The results are interpreted using simplified models of supersymmetry and are expressed in terms of limits on the masses of potential new colored particles. Assuming that the lightest neutralino is stable and has a mass less than about 500 GeV, gluino masses up to 1550-1750 GeV are excluded at 95% confidence level, depending on the gluino decay mechanism. For the scenario of direct production of squark-antisquark pairs, top squarks with masses up to 800 GeV are excluded, assuming a 100% branching fraction for the decay to a top quark and neutralino. Similarly, bottom squark masses are excluded up to 880 GeV, and masses of light-flavor squarks are excluded up to 600-1260 GeV, depending on the degree of degeneracy of the squark masses.

An inclusive search for new physics is performed with a 13 TeV dataset from the CMS detector (May--November 2015, corresponding to 2.32/fb) using events with at least two leptons with the same electrical charge, missing transverse energy, and significant hadronic activity. No significant excesses are reported above the Standard Model background predictions. Constraints are set on a number of new physics models. As motivation, a thorough pedagogical review of the Standard Model and its shortcomings is presented in the first two chapters.

We report on a search for new physics in a final state with two same sign leptons, missing transverse energy, and significant hadronic activity at a center of mass energy $\sqrt{s}$ = 7 TeV. The data were collected with the CMS detector at the CERN LHC and correspond to an integrated luminosity of 0.98 $\mathrm{fb}^{-1}$. Data--driven methods are developed to estimate the dominant Standard Model backgrounds. No evidence for new physics is observed. The dominant background to the analysis comes from failures of lepton identification in Standard Model $t\bar{t}$ events. The $t\bar{t}$ production cross section in the dilepton final state is measured using 3.1 $\mathrm{fb}^{-1}$ of data. The cross section is measured to be 194 $\pm$ 72 (stat) $\pm$ 24 (syst) $\pm$ 21 (lumi) pb. An algorithm is developed that uses tracking information to improve the reconstruction of missing transverse energy. The reconstruction of missing transverse energy is commissioned using the first collisio ns recorded at 0.9, 2.36 and 7 TeV data. Events with abnormally large values of missing transverse energy are identified as arising from anomalous signals in the calorimeters. Tools are developed to identify and remove these anomalous signals.

"An inclusive search for supersymmetric processes that produce final states with jets and missing transverse energy is performed in pp collisions at a center-of-mass energy of [the square root of] s = 8 TeV. The data sample corresponds to an integrated luminosity of 19.5 fb−1 collected by the CMS experiment at the LHC. In this search, a dimensionless kinematic variable, [alpha]T, is used to discriminate between events with genuine and misreconstructed missing transverse energy. The search is based on an examination of the number of reconstructed jets per event, the scalar sum of transverse energies of these jets, and the number of these jets identified as originating from bottom quarks. The results are interpreted in two simplified models with direct stop production"--Page v.

This thesis presents several studies of monophoton final states using 35.9 fb^-1 of 13 TeV proton-proton collision data collected by the CMS experiment at the LHC in 2016. The standard model Z([small nu] [small n̄ū])[small gamma] cross section is measured as a function of photon transverse momentum. No significant deviations from standard model predictions are observed. The results are also interpreted in the context of several new physics models. Limits are placed on new particle masses in simplified models of dark matter, the suppression scale of a dark matter effective field theory model, and the graviton mass scale in a model of extra spatial dimensions.

Dijet events produced in LHC proton-proton collisions at a center-of-mass energy \(\sqrt{s}=8\) TeV are studied with the ATLAS detector using the full 2012 data set, with an integrated luminosity of 20.3 fb-1. Dijet masses up to about 4.5 TeV are probed. Resonancelike features are not observed in the dijet mass spectrum. Limits on the cross section times acceptance are set at the 95% credibility level for various hypotheses of new phenomena in terms of mass or energy scale, as appropriate. This analysis excludes excited quarks with a mass below 4.06 TeV, color-octet scalars with a mass below 2.70 TeV, heavy W' bosons with a mass below 2.45 TeV, chiral W* bosons with a mass below 1.75 TeV, and quantum black holes with six extra space-time dimensions with threshold mass below 5.66 TeV.