Search For Z Bosons Decaying Into Tau Pairs In Pp Collisions At Raiz Cuadrada S
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| Author | : Carlos Felipe González Hernández |
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| Release | : 2018 |
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New heavy neutral gauge bosons, generically referred as Z0 bosons, are predicted in several theoretical scenarios beyond the standard model (BSM). In these kinds of scenarios, the breaking of extended symmetry usually results in an extra U(1)' symmetry group. This additional symmetry would give rise to the existence of a Z' boson with a mass that should be in the TeV scale. There are some scenarios that predict a generational coupling dependence, where the Z' boson would decay preferentially to the third generation of fermions, for instance, the topcolor-assisted technicolor (TAT) models. These scenarios are a motivation to search for Z' bosons decaying into tau pairs. The search for Z' decaying into tau-pairs involves four experimental signatures since the tau lepton can decay leptonically or hadronically. The dihadronic tau channel has the best sensitivity since it has the highest expected signal yield, but it has a high background contribution coming...
| Author | : Andrew Gerard Leister |
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| Total Pages | : 352 |
| Release | : 2015 |
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| Total Pages | : 27 |
| Release | : 2014 |
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| Release | : 2013 |
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We present a measurement of the production cross section for ZW and ZZ boson pairs in final states with a pair of charged leptons, from the decay of a Z boson, and at least two jets, from the decay of a W or Z boson, using the full sample of proton-antiproton collisions recorded with the CDF II detector at the Tevatron, corresponding to 8.9 fb(̂-1) of integrated luminosity. We increase the sensitivity to vector boson decays into pairs of quarks using a neural network discriminant that exploits the differences between the spatial spread of energy depositions and charged-particle momenta contained within the jet of particles originating from quarks and gluons. Additionally, we employ new jet energy corrections to Monte Carlo simulations that account for differences in the observed energy scales for quark and gluon jets. The number of signal events is extracted through a simultaneous fit to the dijet mass spectrum in three classes of events: events likely to contain jets with a heavy-quark decay, events likely to contain jets originating from light quarks, and events that fail these identification criteria. We determine the production cross section to be 2.5 +2.0 -1.0 pb (
| Author | : Noam Tal Hod |
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| Total Pages | : 372 |
| Release | : 2013 |
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| Total Pages | : 173 |
| Release | : 2005 |
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We present the results of a search for new particles decaying to tau pairs using the data corresponding to an integrated luminosity of 195 pb−1 collected from March 2002 to September 2003 with the CDF detector at the Tevatron. Hypothetical particles, such as Z' and MSSM Higgs bosons can potentially produce the tau pair final state. We discuss the method of tau identification, and show the signal acceptance versus new particle mass. The low-mass region, dominated by Z → [tau][tau], is used as a control region. In the high-mass region, we expect 2.8 ± 0.5 events from known background sources, and observe 4 events in the data sample. Thus no significant excess is observed, and we set upper limits on the cross section times branching ratio as a function of the masses of heavy scalar and vector particles.
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| Total Pages | : 0 |
| Release | : 2012 |
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This thesis describes a study of the tau-pair final state in proton collisions at a center of mass energy of 7 TeV using the CMS Experiment at the CERN Large Hadron Collider. Tau leptons usually decay to hadrons and their efficient detection is very challenging in a hadronic environment. A novel tau reconstruction algorithm that maintains tau detection efficiency for low background rates was developed. Events were then selected from the CMS 2011 data sample in three T T final states depending on the tau decays: mu + T (h), e+ T (h), e+mu where T (h) denotes a hadronic tau decay. Those events were used to measure the Z-boson production cross section where Z yields T T . A search for the Standard Model and Minimal Supersymmetric Standard Model (MSSM) Higgs bosons was also performed. No signal was observed in the Higgs search and stringent new bounds were set for the SM Higgs production and in the MSSM parameter space.
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| Release | : 2016 |
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The production of Z bosons with one or two isolated high-energy photons is studied using pp collisions at √s=8 TeV. The analyses use a data sample with an integrated luminosity of 20.3 fb-1 collected by the ATLAS detector during the 2012 LHC data taking. The Z? and Z?? production cross sections are measured with leptonic (e+e-, ?+?-, ?????????) decays of the Z boson, in extended fiducial regions defined in terms of the lepton and photon acceptance. They are then compared to cross-section predictions from the Standard Model, where the sources of the photons are radiation off initial-state quarks and radiative Z-boson decay to charged leptons, and from fragmentation of final-state quarks and gluons into photons. The yields of events with photon transverse energy ET > 250 GeV from l+l-? events and with ET > 400 GeV from ?????????? events are used to search for anomalous triple gauge-boson couplings ZZ? and Z??. The yields of events with diphoton invariant mass m?? > 200 GeV from l+l-?? events and with m?? > 300 GeV from ??????????? events are used to search for anomalous quartic gauge-boson couplings ZZ?? and Z???. As a result, no deviations from Standard Model predictions are observed and limits are placed on parameters used to describe anomalous triple and quartic gauge-boson couplings.
| Author | : Eric Charles Torrence |
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| Total Pages | : 223 |
| Release | : 1997 |
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| Total Pages | : 0 |
| Release | : 2012 |
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A search for exotic particles decaying via WZ to final states with electrons and muons is performed using a data sample of pp collisions collected at 7 TeV center-of-mass energy by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.98 fb-1. A cross section measurement for the production of WZ is also performed on a subset of the collision data. No significant excess is observed over the Standard Model background, so lower bounds at the 95% confidence level are set on the production cross sections of hypothetical particles decaying to WZ in several theoretical scenarios. Assuming the Sequential Standard Model, W' bosons with masses below 1143 GeV/c2 are excluded. New limits are also set for several configurations of Low-Scale Technicolor.
