Search for Multi-lepton Events from Strong and Electroweak SUSY Production in Pp Collisions at a [center-of-mass Energy] of 7 TeV PDF Download

Author: Peter Thomassen
Publisher:
ISBN:
Category : Leptons (Nuclear physics)
Languages : en
Pages : 44

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Author: Robert Wayne Stringer
Publisher:
ISBN: 9781124771816
Category : Gauge fields (Physics)
Languages : en
Pages : 176

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Many theoretical models of physics beyond the Standard Model provide a signature of two photons and large missing transverse energy [Special characters omitted.] in the final state. This search was performed using 36 pb[superscript -1] of proton-proton collision data at [Squared root of s] = 7 TeV. The candidate events are determined by comparing the [Special characters omitted.] distribution for events with two photons and at least one hadronic jet with the [Special characters omitted.] T distribution from QCD and electroweak processes that have no true missing transverse energy. 1.2 ± 0.8 background events were expected, with one event observed. This result was interpreted in two theoretical models beyond the Standard Model. The cross section for General Gauge Mediated Supersymmetry Breaking is given an upper limit between 0.3 pb and 1.1 pb. Universal Extra Dimensions has been excluded for all values of 1/ R

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 13

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One of the most striking signature of supersymmetric models with electroweak symmetry breaking is the presence of multilepton event topologies in the decay products. In this paper searches are presented for physics beyond the Standard Model (SM) in final states containing charged leptons from proton-antiproton collision data at a center-of-mass energy of 1.96 TeV, collected with Run II CDF and D0 Detectors in 2002-2006, and corresponding to integrated luminosities of up to 1.1 fb−1. In any of the searches no excess of candidates was observed with respect to the SM predictions and limits on masses and production cross-sections are set at the 95% CL.

Author:
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ISBN:
Category :
Languages : en
Pages : 39

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A new measurement of the inclusive production cross section for pp to t t-bar is performed at a center-of-mass energy of 7 TeV using data collected by the CMS experiment at the LHC. The analysis uses a data sample corresponding to an integrated luminosity of 36 inverse picobarns, and is based on the final state with one isolated, high transverse momentum muon or electron, missing transverse energy, and hadronic jets. The ttbar content of the selected events is enhanced by requiring the presence of at least one jet consistent with b-quark hadronization. The measured cross section is 150 +/- 9 (stat.) +/- 17 syst.) +/- 6 (lumi.) pb and is in agreement with higher-order QCD calculations. The combination of this measurement with a previous CMS result based on dileptons gives 154 +/- 17 (stat.+syst.) +/- 6 (lumi.) pb.

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

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A search for physics beyond the standard model in events with at least three leptons is presented. The data sample, corresponding to an integrated luminosity of 19.5 inverse femtobarns of proton-proton collisions with center-of-mass energy sqrt(s) = 8 TeV, was collected by the CMS experiment at the LHC during 2012. The data are divided into exclusive categories based on the number of leptons and their flavor, the presence or absence of an opposite-sign, same-flavor lepton pair (OSSF), the invariant mass of the OSSF pair, the presence or absence of a tagged bottom-quark jet, the number of identified hadronically decaying tau leptons, and the magnitude of the missing transverse energy and of the scalar sum of jet transverse momenta. The numbers of observed events are found to be consistent with the expected numbers from standard model processes, and limits are placed on new-physics scenarios that yield multilepton final states. In particular, scenarios that predict Higgs boson production in the context of supersymmetric decay chains are examined. We also place a 95% confidence level upper limit of 1.3% on the branching fraction for the decay of a top quark to a charm quark and a Higgs boson (t to c H), which translates to a bound on the left- and right-handed top-charm flavor-violating Higgs Yukawa couplings, lambda[H, tc] and lambda[H, ct], respectively, of sqrt(abs(lambda[H, tc])2̂ + abs(lambda[H, ct])2̂)

Author: Scott Wilbur
Publisher:
ISBN: 9781267071606
Category :
Languages : en
Pages : 89

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A search is presented for anomalous production of events containing multiple low-energy leptons produced in association with a W or Z boson using the Collider Detector at Fermilab. The leptons are not required to be isolated, and the signature is therefore sensitive to a wide range of so-called "lepton jet" topologies. The search uses data corresponding to 5.1 fb--1 of integrated luminosity from pp ̄ collisions at a center-of-mass energy of s = 1.96 TeV. The observed events are compared with the standard model predictions in bins of additional electron and muon multiplicity. No indications are found of phenomena beyond the standard model. A 95% confidence level limit is presented on the production cross section for an example benchmark point of a dark-matter inspired model of supersymmetric hidden valley Higgs production. Object identification efficiencies are also provided in order to enable the calculation of limits on additional models.

Author:
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ISBN:
Category :
Languages : en
Pages : 29

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A search for excited leptons is carried out with the CMS detector at the LHC, using 36 inverse picobarns of pp collision data recorded at sqrt(s) = 7 TeV. The search is performed for associated production of a lepton and an oppositely charged excited lepton pp to l l*, followed by the decay l* to l gamma, resulting in the l l gamma final state, where l = electron or muon. No excess of events above the standard model expectation is observed. Interpreting the findings in the context of l* production through four-fermion contact interactions and subsequent decay via electroweak processes, first upper limits are reported for l* production at this collision energy. The exclusion region in the compositeness scale Lambda and excited lepton mass M(l*) parameter space is extended beyond previously established limits. For Lambda = M(l*), excited lepton masses are excluded below 1070 GeV/c2̂ for e* and 1090 GeV/c2̂ for mu* at the 95% confidence level.

Author: Waruna Sri Fernando
Publisher:
ISBN:
Category :
Languages : en
Pages : 110

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Abstract: We present a search for the lepton flavor violating decay Z->eu in proton-proton collisions at a center of mass energy of 7 TeV using approximately 3.1 pb−1 of data recorded with the ATLAS detector at the CERN large hadron collider. Candidate events have two isolated high p[tau] leptons (an electron and a muon), no jets, and little missing transverse energy. We observe no events with eu invariant mass above 60 GeV/c2. This demonstrates that we can suppress the eu background to a negligible level and are sensitive to exotic eu production. We set 95% confidence upper limit on the Z->eu branching ratio of 2.0 x 10−4.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 7

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Book Description
The authors report a search for the anomalous production of events with multiple charged leptons in p{bar p} collisions at √s = 1.96 TeV using a data sample corresponding to an integrated luminosity of 346 pb−1 collected by the CDF II detector at the Fermilab Tevatron. The search is divided into three-lepton and four-or-more-lepton data samples. They observe six events in the three-lepton sample and zero events in the ≥4-lepton sample. Both numbers of events are consistent with standard model background expectations. Within the framework of an R-parity violating supergravity model, the results are interpreted as mass limits on the lightest neutralino ({bar {chi}}1°) and chargino ({bar {chi}}1{sup {+-}}) particles. For one particular choice of model parameters, the limits are M({bar {chi}}1°) > 110 GeV/c2 and M({bar {chi}}1{sup {+-}}) > 203 GeV/c2 at 95% confidence level; the variation of these mass limits with model parameters is presented.

Author: Lesya Horyn
Publisher: Springer Nature
ISBN: 3030916723
Category : Science
Languages : en
Pages : 146

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Book Description
This thesis presents a search for long-lived particles decaying into displaced electrons and/or muons with large impact parameters. This signature provides unique sensitivity to the production of theoretical lepton-partners, sleptons. These particles are a feature of supersymmetric theories, which seek to address unanswered questions in nature. The signature searched for in this thesis is difficult to identify, and in fact, this is the first time it has been probed at the Large Hadron Collider (LHC). It covers a long-standing gap in coverage of possible new physics signatures. This thesis describes the special reconstruction and identification algorithms used to select leptons with large impact parameters and the details of the background estimation. The results are consistent with background, so limits on slepton masses and lifetimes in this model are calculated at 95% CL, drastically improving on the previous best limits from the Large Electron Positron Collider (LEP).