Search for Supersymmetry Using a Photon, B-jets, and E MissT Final State with the ATLAS Detector in Proton-proton Collisions at 8TeV Center-of-mass Energy PDF Download

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ISBN: 9781321676105
Category :
Languages : en
Pages : 207

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The result of this analysis is interpreted in a general gauge mediation framework with a lightest neutralino that is a mixture of bino and higgsino. Limits are set in a 2D plane of gluino mass vs neutralino mass. Neutralino masses between 150 GeV and 450 GeV are excluded at 95% CL for all gluino masses, and gluino masses up to at least 1200 GeV (and up to 1350 GeV in some cases) are excluded at 95% CL for neutralino masses between 450 GeV and 50 GeV less than the gluino mass.

Author: Paul B. Geffert
Publisher:
ISBN: 9781321349412
Category :
Languages : en
Pages : 257

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This thesis describes a search for supersymmetry in events with a single lepton, large jet multiplicity, multiple b jets, and significant transverse momentum imbalance in 19.3 fb-1 of pp collisions at center of mass energy of 8 TeV recorded in 2012 by the Compact Muon Solenoid experiment at the Large Hadron Collider. This signature targets strongly produced massive gluinos which decay through top squarks. The observed yields in the signal regions, spanning a broad range of event kinematics, agree with the Standard Model background predictions, which are obtained with a heavy reliance on data control samples. The results of this search are interpreted as cross section limits in the context of simplified supersymmetric scenarios in which gluinos are pair produced and cascade decay to a four top quark, two lightest neutralino final state. By comparing these limits with gluino pair production cross sections, gluinos with mass less than 1 TeV are excluded for low lightest neutralino masses, largely independent of top squark mass.

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Category :
Languages : en
Pages : 23

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The results of a search for new physics in final states with jets, either photons or leptons, and low missing transverse momentum are reported. The study is based on a sample of proton-proton collisions collected at a center-of-mass energy View the MathML source with the CMS detector in 2012. The integrated luminosity of the sample is 19.7 fb-1. Many models of new physics predict the production of events with jets, electroweak gauge bosons, and little or no missing transverse momentum. Examples include stealth models of supersymmetry (SUSY), which predict a hidden sector at the electroweak energy scale in which SUSY is approximately conserved. Furthermore, the data are used to search for stealth SUSY signatures in final states with either two photons or an oppositely charged electron and muon. No excess is observed with respect to the standard model expectation, and the results are used to set limits on squark pair production in the stealth SUSY framework.

Author: Yutaro Iiyama
Publisher: Springer
ISBN: 3319586610
Category : Science
Languages : en
Pages : 182

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This Ph.D. thesis is a search for physics beyond the standard model (SM) of particle physics, which successfully describes the interactions and properties of all known elementary particles. However, no particle exists in the SM that can account for the dark matter, which makes up about one quarter of the energy-mass content of the universe. Understanding the nature of dark matter is one goal of the CERN Large Hadron Collider (LHC). The extension of the SM with supersymmetry (SUSY) is considered a promising possibilities to explain dark matter. The nominated thesis describes a search for SUSY using data collected by the CMS experiment at the LHC. It utilizes a final state consisting of a photon, a lepton, and a large momentum imbalance probing a class of SUSY models that has not yet been studied extensively. The thesis stands out not only due to its content that is explained with clarity but also because the author performed more or less all aspects of the thesis analysis by himself, from data skimming to limit calculations, which is extremely rare, especially nowadays in the large LHC collaborations.

Author: Tova Ray Holmes
Publisher:
ISBN:
Category :
Languages : en
Pages : 191

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A search for new phenomena in final states containing a Z boson decaying to electrons or muons, jets, and large missing transverse momentum is presented. This search uses proton--proton collision data collected during 2015 and 2016 at a center of mass energy sqrt(s)=13 TeV by the ATLAS detector at the Large Hadron Collider, which correspond to an integrated luminosity of 14.7 fb-1. The search targets the pair production of supersymmetric particles, squarks or gluinos, which decay via jets and a Z boson to the lightest Supersymmetric particle, which does not interact with the ATLAS detector. Results are interpreted in simplified models of gluino-pair (squark-pair) production, and provide sensitivity to gluinos (squarks) with masses as large as 1.3 (1.0) TeV.

Author:
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ISBN:
Category :
Languages : en
Pages :

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Book Description
An inclusive search for supersymmetry in events with at least one b-tagged jet is performed using proton-proton collision data collected by the CMS experiment in 2012 at a center-of-mass energy of 8 TeV. The data set size corresponds to an integrated luminosity of 19.3 fb-1. The two-dimensional distribution of the razor variables R2 and MR is studied in events with and without leptons. The data are found to be consistent with the expected background, which is modeled with an empirical function. Exclusion limits on supersymmetric particle masses at a 95% confidence level are derived in several simplified supersymmetric scenarios for several choices of the branching fractions. Also, by combining the likelihoods of a search in events without leptons and a search that requires a single lepton (electron or muon), an improved bound on the top-squark mass is obtained. By assuming the lightest supersymmetric particle to be stable and weakly interacting, and to have a mass of 100 GeV, the branching-fraction-dependent (-independent) production of gluinos is excluded for gluino masses up to 1310 (1175) GeV. As a result, the corresponding limit for top-squark pair production is 730 (645) GeV.

Author:
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ISBN:
Category :
Languages : en
Pages :

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Results of a search for decays of massive particles to fully hadronic final states are presented. This search uses 20.3 fb-1 of data collected by the ATLAS detector in √8 TeV proton-proton collisions at the LHC. Signatures based on high jet multiplicities without requirements on the missing transverse momentum are used to search for R-parity-violating supersymmetric gluino pair production with subsequent decays to quarks. Our analysis was performed using a requirement on the number of jets, in combination with separate requirements on the number of b-tagged jets, as well as a topological observable formed from the scalar sum of the mass values of large-radius jets in the event. Results were interpreted in the context of all possible branching ratios of direct gluino decays to various quark flavors. No significant deviation is observed from the expected Standard Model backgrounds estimated using jet counting as well as data-driven templates of the total-jet-mass spectra. Gluino pair decays to ten or more quarks via intermediate neutralinos are excluded for a gluino with mass mg ̃ 1 TeV for a neutralino mass msub?0̃ 1/sub = 500 GeV. Direct gluino decays to six quarks are excluded for msubg

Author: Eun Sin Lee
Publisher:
ISBN:
Category :
Languages : en
Pages :

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This dissertation presents the results of a search for supersymmetry in protonantiproton collisions with a center of mass energy of 1.96 TeV studied with the Collider Detector at Fermilab. Our strategy is to select collisions with two photons in the final state that have the properties of being the decays of very massive supersymmetric particles. This includes looking for large total energy from the decayed particles as well as for the presence of particles that leave the detector without interacting. We find no events using 2.6 fb−1 of data collected during the 2004-2008 collider run of the Fermilab Tevatron which is consistent with the background estimate of 1.4 " 0.4 events. Since there is no evidence of new particles we set cross section limits in a gaugemediated supersymmetry model with X01 ---> [gamma]G, where the X01 and G are the lightest neutralino and the gravitino (the lightest supersymmetric particle), respectively. We set limits on models as a function of the X01 mass and lifetime, producing the world's most sensitive search for X01 by excluding masses up to 149 GeV/c2 for X01 lifetimes much less than 1 ns.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 234

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Book Description
This dissertation presents the results of a search for supersymmetry in proton-antiproton collisions with a center of mass energy of 1.96 TeV studied with the Collider Detector at Fermilab. Our strategy is to select collisions with two photons in the final state that have the properties of being the decays of very massive supersymmetric particles. This includes looking for large total energy from the decayed particles as well as for the presence of particles that leave the detector without interacting. We find no events using 2.6 fb−1 of data collected during the 2004-2008 collider run of the Fermilab Tevatron which is consistent with the background estimate of 1.4 ± 0.4 events. Since there is no evidence of new particles we set cross section limits in a gauge-mediated supersymmetry model with {tilde {chi}}1° → [gamma]{tilde G}, where the {tilde {chi}}1° and {tilde G} are the lightest neutralino and the gravitino (the lightest supersymmetric particle), respectively. We set limits on models as a function of the {tilde {chi}}1° mass and lifetime, producing the world's most sensitive search for {tilde {chi}}1° by excluding masses up to 149 GeV/c2 for {tilde {chi}}1° lifetimes much less than 1 ns.

Author: Mats Joakim Robert Olsson
Publisher:
ISBN: 9780438756403
Category :
Languages : en
Pages : 256

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Book Description
The Large Hadron Collider (LHC) and its experiments were built to explore fundamental questions of particle physics via proton-proton collisions at unprecedented center-of-mass energies, thus providing a unique environment for testing the Standard Model (SM) at the electroweak scale and searching for signs of new physics beyond the SM (BSM). The discovery of a SM-like 125 GeV Higgs boson by ATLAS and CMS hints of new physics at the electroweak scale-possibly within reach of the LHC-in order to mitigate divergent radiative corrections to the Higgs squared mass. This can systematically be accomplished by the introduction of supersymmetry (SUSY). For the experimentalist, SUSY provides a set of simplified benchmark models, with explicit and testable predictions, which are useful when searching for BSM physics. A large number of BSM searches has been carried out at the LHC. However, no evidence for SUSY has been found. It is therefore important to expand the scope. This thesis presents two ATLAS analyses for SUSY, both utilizing fully hadronic final states. The first analysis searches for the pair production of top squarks (stops), each with R-parity-violating decays into a b- and an s-quark. This analysis was performed using proton-proton collision data with an integrated luminosity of 17.4 fb-1 at a center-of-mass energy of 8 TeV. The second analysis searches for electroweak production of a chargino-neutralino pair, decaying into SM-quarks via a W boson and a SM-like 125 GeV Higgs boson, performed using an integrated luminosity of 36.1 fb-1 at a center-of-mass energy of 13 TeV. No evidence of an excess beyond the SM background prediction is observed in either search, thus exclusion limits are set at 95% CL. Stops decaying directly to hadronic final states are excluded for masses in the range 100 to 315 GeV. Charginos and neutralinos decaying via Wh to hadronic final states are excluded up to 680 GeV, by far the strongest limits on electroweak SUSY with Wh decays to date. The tools and strategies developed in the searches for SUSY with hadronic final states in this thesis should prove useful in future searches for BSM physics at the LHC.