A Search for Supersymmetry Via Chargino-neutralino Production in Low-[particle Transverse Momentum] Dimuon Channel with the Collider Detector at Fermilab PDF Download

Author: Vladimir Rekovic
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ISBN:
Category : Leptons (Nuclear physics)
Languages : en
Pages : 466

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Author:
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ISBN:
Category :
Languages : en
Pages : 265

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We have searched for evidence of supersymmetry with 1 $fb^-1$ with collected with low-$p_T$ dimuon triggers of the Collider Detector on Tevatron Run II, at Fermilab. We looked for trilepton events in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV. In the Minimal Supersymmetric Standard Model (MSSM) we expect chargino-neutralino pair production, with subsequent decay into three isolated leptons. We observe one event of three isolated muons, a possible hint of supersymmetry.

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Languages : en
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We have searched for evidence of supersymmetry with the Collider Detector at Fermilab using trilepton events in p[anti p] collisions at[radical]s= 1.8 TeV. In the Minimal Supersymmetric Standard Model (MSSM), we expect trilepton events from chargino-neutralino ([tilde[xi]][sup[+-]][sub 1][tilde[xi]][sup 0][sub 2]) pair production, with subsequent decay into leptons. In all possible combinations of electron and muon channels, we observe no candidate events in 107 pb[sup -1] of data. We present limits on chargino and neutralino production within the framework of a supergravity inspired MSSM:[sigma][sub[tilde[xi]][sup[+-]][sub 1][tilde[xi]][sup 0][sub 2]][center-dot] BR([tilde[xi]][sup[+-]][sub 1][tilde[xi]][sup 0][sub 2][yields] 3l+ X)0.34 pb and M[sub[tilde[xi]][sup[+-]][sub 1]] 81.5 GeV/c[sup 2] for tan[beta]= 2, [mu]= -600 GeV/c[sup 2] and M[sub[tilde q]]= M[sub[tilde g]]. We also present limits on a SU(5) x U(1) supergravity model and a 4 and 1/2 parameter Minimal SUGRA model.

Author: Ulla Blumenschein
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ISBN:
Category :
Languages : en
Pages : 232

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The search for a fundamental theory of matter and forces in the universe has ever since attracted the interest of physicists. The large success of the gauge theories in the description of low-energy phenomena nourishes the hope that gauge symmetries are the clue to a unified description of all fundamental processes at high energy scales. Particle collision experiments of the past decades have probed the structure of matter with increasing resolution. The phenomena observed in collision experiments at current energy scales are described with a large precision by the Standard Model of particle physics. Nevertheless, many open questions in the Standard Model suggest that it is an effective low-energy theory of a more fundamental theory: the numbers of free parameters of the model, the numbers of generations, the hierarchy between the electroweak scale and the Planck scale, the pending integration of gravity and the evolution of the strengths of the fundamental forces at large energy regimes. In addition, recent cosmological data suggest that the density of ordinary matter which is described by the Standard Model, corresponds only to a small fraction of the matter density in the universe. Many of the above mentioned problems are addressed by an extension of the Standard Model that is based on an additional internal symmetry, the Supersymmetry (SUSY) of fermions and bosons. It predicts the existence of a partner for each known fundamental particle with the same quantum numbers but different spin. Supersymmetry must be broken at the energy regime of present collider experiments which leads to different masses of Standard Model particles and their super-partners. Low-mass supersymmetric partners are expected to be produced at a sufficient rate at present or future collider experiments. In the analysis performed in this thesis, it is assumed that SUSY particles decay into their Standard Model partners and the stable lightest supersymmetric particle, which is only weakly interacting, carrying away energy and momentum and leading to detector signatures with large missing energy. Supersymmetric particles have been searched for at the electron-positron collider LEP up to the kinematic limit. No evidence for these particles has been observed which results in lower limits on their masses. Additional constraints stem from precision measurements of quantities, which are sensitive to corrections from SUSY particles and from the search for dark matter in cosmological experiments. The search for SUSY particles beyond the reach of LEP is continued at larger energy regimes at present and future hadron colliders. In its second phase of data taking (Run II), the center-of-mass energy of the proton-antiproton collider Tevatron at Fermilab has been raised and the luminosity has been increased considerably. The D0 experiment, one of the two Tevatron experiments, has been upgraded accordingly. The Tevatron collider allows to probe a substantial SUSY mass range beyond the LEP limits. The search will be continued at the Large Hadron Collider (LHC) which is presently being constructed at the European Research laboratory for particle physics CERN in Geneva. At hadron colliders the supersymmetric partners of quarks and gluons are copiously produced in strong interactions, provided they are light enough. Within most of the established SUSY models, these particles are too heavy to be produced at a sufficient rate at the Tevatron collider and the production of the lighter super-partners of the Higgs and gauge bosons, the charginos and neutralinos, becomes an important source of SUSY particles. Decays of these particles result in final states with leptons or hadrons and large missing energy. Leptonic final states can be separated more easily from the large background of hadronic Standard Model processes. A search for the associated production of the lightest chargino and the second lightest neutralino has been performed in final states with two electrons, an additional lepton and large missing transverse energy using data collected with the D0 detector from April 2002 to July 2004. The results are interpreted stand-alone and in combination with other leptonic channels in the framework of constraint supersymmetric models.

Author:
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ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 980

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Author: Benn Tannenbaum
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Category : Leptons (Nuclear physics)
Languages : en
Pages : 318

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Author: Steven Farrell
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ISBN: 9781303654763
Category :
Languages : en
Pages : 216

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Two searches for supersymmetry in multilepton final states are presented using pp collisions at sqrt(s) = 8 TeV in the ATLAS detector. First, a search for electroweak production of charginos and neutralinos in the three-lepton plus missing transverse momentum channel is detailed with an emphasis on the fake-lepton background estimation technique. No significant excess above the Standard Model prediction is observed in the signal regions. Exclusion limits are thus placed on simplified models of chargino1-neutralino2 production and decays via intermediate sleptons, SM gauge bosons, and Higgs bosons. The results are also interpreted in terms of the phenomenological MSSM. Next, a search for R-parity violating and R-parity conserving supersymmetric scenarios in the four-lepton channel is presented. No significant excess is observed, so exclusion limits are placed R-parity violating simplified models in which the lightest supersymmetric particle is the lightest neutralino, which promptly decays to leptons. Exclusion limits are also placed on R-parity conserving simplified models of neutralino2-neutralino3 production.

Author: John Strologas
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ISBN:
Category :
Languages : en
Pages : 4

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The chargino-neutralino production is one of the most promising SUSY processes that could be observed at the Tevatron. Cross sections of the order of 0.1 pb have not been excluded yet under the mSUGRA scenario, whereas the trilepton signature of the process is not contaminated by significant standard model backgrounds. We report on the status of CDF search for chargino-neutralino production at the Tevatron by presenting the results of five multilepton subanalyses as well as the result of their combination which leads to our current lower limit on the chargino mass of 127 GeV/c{sup 2} and upper limit on the production cross section times branching ratio to leptons of 0.25 pb at 95% confidence level.

Author:
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ISBN:
Category :
Languages : en
Pages : 27

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Results are presented from a search for supersymmetric particles in scenarios with a compressed mass spectrum. The data sample corresponds to 19.7 inverse femtobarns of proton-proton collisions recorded by the CMS experiment at √s = 8 TeV. The search targets top squark ($ ilde{t}$ pair production in scenarios with mass differences ?m = m($ ilde{t}$ – m($ ilde{i}$10) below the W-boson mass and with top-squark decays in the four-body mode ($ ilde{t}$ → blv$ ilde{i}$10), where the ($ ilde{i}$10) is assumed to be the lightest supersymmetric particle (LSP). The signature includes a high transverse momentum (pT) jet associated with initial-state radiation, one or two low-pT leptons, and significant missing transverse energy. The event yields observed in data are consistent with the expected background contributions from standard model processes. Limits are set on the cross section for top squark pair production as a function of the $ ilde{t}$ and LSP masses. Assuming a 100% branching fraction for the four-body decay mode, top-squark masses below 316 GeV are excluded for ?m = 25 GeV at 95% CL. Furthermore, the dilepton data are also interpreted under the assumption of chargino-neutralino production, with subsequent decays to sleptons or sneutrinos. Assuming a difference between the common $ ilde{i}$1+/$ ilde{i}$2+ mass and the LSP mass of 20 GeV and a ?-enriched decay scenario, masses in the range m( $ ilde{i}$1+)

Author:
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Category :
Languages : en
Pages :

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This article presents the current experimental results of searches for Supersymmetry (SUSY) at the Collider Detector at Fermilab (CDF), using over 110 pb−1 of proton-antiproton collision data with (square root)s = 1800 GeV collected during the period 1992-1995. Since no signal was found, limits on the production of supersymmetric particles are derived. The prospects for supersymmetry searches at Run II of the Tevatron, that began in March 2001, are also discussed here.