"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.

CMS results of a new physics search in same-sign dilepton events with b-tagged jets and missing transverse energy (MET) are being presented. These results cover the full 2012 dataset from the LHC at root(s)=8 TeV, corresponding to 19.5/fb. Isolated same-sign dilepton events are easily detected and rare in the Standard Model (SM), but they occur in abundance in some supersymmetry (SUSY) models. Hence, this channel provides a very clean, low background, search for new physics. Multiple search regions defined by the observables MET, hadronic energy (HT), and number of b-tagged jets are considered. The data agrees with the SM prediction, therefore exclusion limits at 95% C.L. are presented for various simplified SUSY models.

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.

This thesis describes the use of the angular distributions of the most energetic dijets in data recorded by the ATLAS experiment, at CERN’s Large Hadron Collider (LHC), the goal of which is to search for phenomena beyond what the current theory of Particle Physics (the Standard Model) can describe. It also describes the deployment of the method used in ATLAS to correct for the distortions in jet energy measurements caused by additional proton–proton interactions. The thesis provides a detailed introduction to understanding jets and dijet searches at the LHC. The experiments were carried out at two record collider centre-of-mass energies (8 and 13 TeV), probing smaller distances than ever before. Across a broad momentum transfer range, the proton constituents (quarks and gluons) display the same kinematical behaviour, and thus still appear to be point-like. Data are compared to predictions corrected for next-to-leading order quantum chromodynamics (NLO QCD) as well as electroweak effects, demonstrating excellent agreement. The results are subsequently used to set limits on parameters of suggested theoretical extensions to the Standard Model (SM), including the effective coupling and mass of a Dark Matter mediator.

An inclusive search for supersymmetric processes that produce final states with jets and missing transverse energy is performed in pp collisions at a centre-of-mass energy of 8 TeV. The data sample corresponds to an integrated luminosity of 11.7 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. No significant excess of events over the standard model expectation is found. Exclusion limits are set in the parameter space of simplified models, with a special emphasis on both compressed-spectrum scenarios and direct or gluino-induced production of third-generation squarks. For the case of gluino-mediated squark production, gluino masses up to 950-1125 GeV are excluded depending on the assumed model. Finally, for the direct pair-production of squarks, masses up to 450 GeV are excluded for a single light first- or second-generation squark, increasing to 600 GeV for bottom squarks.

This thesis describes in detail the search for new phenomena in mono-jet final states with the ATLAS experiment at the LHC. The final state is considered the golden channel in the searches for large extra dimensions (LED) but also allows access to a very rich SUSY-related phenomenology pertaining to the production of weakly interacting massive particles (WIMPS), SUSY Dark Matter candidates, GMSB SUSY models with very light gravitino masses, as well as stop an sbottom pair production in compressed scenarios (with nearly degenerated squarks and the lightest neutralino), and also invisible Higgs searches, among others. Here, a number of these scenarios are explored. The measurements presented yield new powerful constraints on the existence of extra spatial dimensions, the pair production of WIMPs, and also provide the best limit to date on the gravitino mass.

A search for new physics is performed based on events with jets and a pair of isolated, same-sign leptons. The results are obtained using a sample of proton-proton collision data collected by the CMS experiment at a centre-of-mass energy of 8 TeV at the LHC, corresponding to an integrated luminosity of 19.5 inverse femtobarns. In order to be sensitive to a wide variety of possible signals beyond the standard model, multiple search regions defined by the missing transverse energy, the hadronic energy, the number of jets and b-quark jets, and the transverse momenta of the leptons in the events are considered. No excess above the standard model background expectation is observed and constraints are set on a number of models for new physics, as well as on the same-sign top-quark pair and quadruple-top-quark production cross sections. As a result, information on event selection efficiencies is also provided, so that the results can be used to confront an even broader class of new physics models.