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This thesis presents a search for evidence of new supersymmetric particles in proton-proton collision data collected by the Compact Muon Solenoid at the Large Hadron Collider located in Geneva, Switzerland. The data was collected in 2012 at a center of mass energy of 8 TeV and corresponds to an integrated luminosity of 19.5 inverse femtobarns. The search examines events that produce the experimental signature of a disappearing track. Disappearing tracks are identifed as those with little or no associated calorimeter energy deposits and with several missing hits in the outer layers of the tracker. This search is motived by anomaly-mediated supersymmetry which postulates that a long-lived chargino decaying to a neutralino and pion with low momentum could give rise to a disappearing track. The sources of background in this search arise from leptons which fail to be reconstructed and false trajectories determined by the track reconstruction algorithm. The number of observed events is in agreement with the background expectation, and limits are set on the cross section of direct electroweak chargino production in terms of the chargino mass and mean proper lifetime. At 95 % confidence level, anomaly-mediated supersymmetry breaking models with a chargino mass less than 260 GeV, corresponding to a mean proper lifetime of 0.2 ns, are excluded.
A search is presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track. Disappearing tracks are identified as those with little or no associated calorimeter energy deposits and with missing hits in the outer layers of the tracker. The search uses proton-proton collision data recorded at [arrow]" = 8 TeV that corresponds to an integrated luminosity of 19.5 fb-1. The results of the search are interpreted in the context of the anomaly-mediated supersymmetry breaking (AMSB) model. The number of observed events is in agreement with the background expectation, and limits are set on the cross section of direct electroweak chargino production in terms of the chargino mass and mean proper lifetime. At 95% confidence level, AMSB models with a chargino mass less than 260 GeV, corresponding to a mean proper lifetime of 0.2 ns, are excluded.
A search is presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track. A disappearing track is an isolated track with no associated hits in the muon detectors, small associated calorimeter energy deposits, and missing hits in the outer layers of the silicon tracker. The search uses 38.4 fb-1 of proton-proton collision data collected by the CMS detector in 2015 and 2016, at a center-of-mass energy of 13 TeV at the CERN LHC. The results of the search are interpreted in the context of anomaly-mediated supersymmetry breaking. The observation is consistent with the background-only hypothesis, and limits are set on the product of the cross section of direct chargino production and the branching fraction to a neutralino and a pion in terms of the chargino mass and lifetime. At 95% confidence level, charginos with masses less than 715 GeV are excluded for a lifetime of 3 ns.
Results are presented from a search for new decaying massive particles whose presence is inferred from an imbalance in transverse momentum and which are produced in association with a single top quark that decays into a bottom quark and two light quarks. The measurement is performed using 19.7 fb-1 of data from proton-proton collisions at a center-of-mass energy of 8 TeV, collected with the CMS detector at the CERN LHC. No deviations from the standard model predictions are observed and lower limits are set on the masses of new invisible bosons. In particular, scalar and vector particles, with masses below 330 and 650 GeV, respectively, are excluded at 95% confidence level, thereby substantially extending a previous limit published by the CDF Collaboration.
A search for the decay of a light Higgs boson to a pair of weakly-interacting, long-lived particles in 20.8 fb-1 of proton-proton collisions at [square root of] s = 8 TeV recorded in 2012 by the ATLAS detector is presented. The strategy requires that both of the long-lived particles decay just before or inside the hadronic calorimeter. No statistically significant excess of events is observed above the expected background and limits on the Higgs boson production and branching ratio to weakly-interacting, long-lived particles are derived as a function of the particle's proper decay length.
Results are reported from a search for R-parity violating supersymmetry in proton-proton collision events collected by the CMS experiment at a center-of-mass energy of sqrt(s)=8 TeV. The data sample corresponds to an integrated luminosity of 17.6 inverse femtobarns. This search assumes a minimal flavor violating model in which the lightest supersymmetric particle is a long-lived neutralino or gluino, leading to a signal with jets emanating from displaced vertices. In a sample of events with two displaced vertices, no excess yield above the expectation from standard model processes is observed, and limits are placed on the pair production cross section as a function of mass and lifetime of the neutralino or gluino. At 95% confidence level, the analysis excludes cross sections above approximately 1 fb for neutralinos or gluinos with mass between 400 and 1500 GeV and mean proper decay length between 1 and 30 mm. Assuming gluino pair production cross sections, gluino masses are excluded below 1 and 1.3 TeV for mean proper decay lengths of 300 micrometers and 1 mm, respectively, and below 1.4 TeV for the range 2-30 mm. The results are also applicable to other models in which long-lived particles decay into multijet final states.