Search for W' {u2192} Tb{u00AF} in the Lepton Plus Jets Final State in Proton-proton Collisions at a Centre-of-mass Energy of {u221A}s

Search for W' {u2192} Tb{u00AF} in the Lepton Plus Jets Final State in Proton-proton Collisions at a Centre-of-mass Energy of {u221A}s
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Total Pages: 21
Release: 2015
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In this study, a search for new charged massive gauge bosons, called W', is performed with the ATLAS detector at the LHC, in proton–proton collisions at a centre-of-mass energy of √s=8 TeV, using a dataset corresponding to an integrated luminosity of 20.3 fb-1. This analysis searches for W' bosons in the W' → tb¯ decay channel in final states with electrons or muons, using a multivariate method based on boosted decision trees. The search covers masses between 0.5 and 3.0 TeV, for right-handed or left-handed W' bosons. No significant deviation from the Standard Model expectation is observed and limits are set on the W' → tb¯ cross-section times branching ratio and on the W'-boson effective couplings as a function of the W'-boson mass using the CLs procedure. For a left-handed (right-handed) W' boson, masses below 1.70 (1.92) TeV are excluded at 95% confidence level.

Search for W' {u2192} Tb in Proton-proton Collisions at $ \sqrt{s}

Search for W' {u2192} Tb in Proton-proton Collisions at $ \sqrt{s}
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Total Pages:
Release: 2016
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A search for dark matter particles directly produced in proton-proton collisions recorded by the CMS experiment at the LHC is presented. The data correspond to an integrated luminosity of 18.8 inverse femtobarns, at a center-of-mass energy of 8 TeV. The event selection requires at least two jets and no isolated leptons. The razor variables are used to quantify the transverse momentum balance in the jet momenta. The study is performed separately for events with and without jets originating from b quarks. The observed yields are consistent with the expected backgrounds and, depending on the nature of the production mechanism, dark matter production at the LHC is excluded at 90% confidence level for a mediator mass scale Lambda below 1 TeV. The use of razor variables yields results that complement those previously published.

Search for W' $\to $ Tb Decays in the Lepton + Jets Final State in Pp Collisions at $\sqrt{s}$

Search for W' $\to $ Tb Decays in the Lepton + Jets Final State in Pp Collisions at $\sqrt{s}$
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Total Pages: 35
Release: 2014
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Results are presented from a search for the production of a heavy gauge boson W' decaying into a top and a bottom quark, using a data set collected by the CMS experiment at sqrt(s) = 8 TeV and corresponding to an integrated luminosity of 19.5 inverse femtobarns. Various models of W'-boson production are studied by allowing for an arbitrary combination of left- and right-handed couplings. The analysis is based on the detection of events with a lepton (e, mu), jets, and missing transverse energy in the final state. No evidence for W'-boson production is found and 95% confidence level upper limits on the production cross section times branching fraction are obtained. For W' bosons with purely right-handed couplings, and for those with left-handed couplings assuming no interference effects, the observed 95% confidence level limit is M(W')> 2.05 TeV. For W' bosons with purely left-handed couplings, including interference effects, the observed 95% confidence level limit is M(W')> 1.84 TeV. The results presented in this paper are the most stringent limits published to date.

Observation of Top-quark Pair Production in Association with a Photon and Measurement of the Tt{u00AF}? Production Cross Section in pp Collisions at {u221A}s

Observation of Top-quark Pair Production in Association with a Photon and Measurement of the Tt{u00AF}? Production Cross Section in pp Collisions at {u221A}s
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Release: 2015
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A search is performed for top-quark pairs (tt¯) produced together with a photon (?) with transverse energy greater than 20 GeV using a sample of tt¯ candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of 4.59 fb−1 of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total, 140 and 222 tt¯? candidate events are observed in the electron and muon channels, to be compared to the expectation of 79 ± 26 and 120 ± 39 non-tt¯? background events, respectively. The production of tt¯? events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The tt¯? production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is ?fidtt¯? × BR = 63 ± 8(stat)+17–13(syst) ± 1(lumi) fb per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of 48 ± 10 fb.

Search for ZW/ZZ Going to Lepton+ Lepton- Jets Production in Proton-proton Collisions at CDF.

Search for ZW/ZZ Going to Lepton+ Lepton- Jets Production in Proton-proton Collisions at CDF.
Author: Wesley Ketchum
Publisher:
Total Pages: 235
Release: 2012
Genre:
ISBN: 9781267835192

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The Standard Model of particle physics describes weak interactions mediated by massive gauge bosons that interact with each other in well-defined ways. Observations of the production and decay of WW, WZ, and ZZ boson pairs are an opportunity to check that these self-interactions agree with the Standard Model predictions. Furthermore, final states that include quarks are very similar to the most prominent final state of Higgs bosons produced in association with a W or Z boson. Diboson production where WW is a significant component has been observed at the Tevatron collider in semi-hadronic decay modes. We present a search for ZW and ZZ production in a final state containing two charged leptons and two jets using 8.9 fb−1 of data recorded with the CDF detector at the Tevatron. We select events by identifying those that contain two charged leptons, two hadronic jets, and low transverse missing energy ( E /T ). We increase our acceptance by using a wide suite of high- pT lepton triggers and by relaxing many lepton identification requirements. We develop a new method for calculating corrections to jet energies based on whether the originating parton was a quark or gluon to improve the agreement between data and the Monte Carlo simulations used to model our diboson signal and dominant backgrounds. We also make use of neural-network-based discriminants that are trained to pick out jets originating from b quarks and light-flavor quarks, thereby increasing our sensitivity to Z → bb ̄ and W/Z → qq ̄' decays, respectively. The number of signal events is extracted through a simultaneous fit to the dijet mass spectrum in three channels: a heavy-flavor tagged channel, a light-flavor tagged channel, and an untagged channel. We measure σZW/ZZ = 2.5+2.0-1.0 pb, which is consistent with the SM cross section of 5.1 pb. We establish an upper limit on the cross section of σZW/ZZ

Search for (W/Z {u2192} Jets) + ? Events in Proton-Antiproton Collisions at the Fermilab Tevatron

Search for (W/Z {u2192} Jets) + ? Events in Proton-Antiproton Collisions at the Fermilab Tevatron
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Total Pages: 160
Release: 2005
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ISBN:

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We present a study of the p¯p → W(Z)? → ?q¯q process at the center-of-mass energy √s = 1.96 TeV using data collected by the Collider Detector at Fermilab. The analysis is based on the selection of low transverse momentum photons produced in association with at least two jets. A modification of an existing photon trigger was studied and implemented in the data acquisition system to enhance the sensitivity of this analysis. The data presented are from approximately 184 pb-1 of integrated luminosity collected by this new trigger. A preliminary event sample is obtained requiring a central photon with ET > 12 GeV and two jets with ET > 15 GeV. The corresponding efficiency is studied using a Monte Carlo simulation of the W(Z)? → ?q¯q based on Standard Model predictions. Monte Carlo estimation of the background is not necessary as it is measured from the data. A more advanced selection based on a Neural Network method improves the signal-to-noise ratio from 1/333 to 1/71, and further optimization of the dijet mass search region increases the ratio to its final value of 1/41. No evidence of a W/Z → q¯q peak in the dijet mass distribution is visible when the background contribution is subtracted. Using a fully Bayesian approach, the 95% confidence level upper limit on ?(p¯p → W?) x ?(W → q¯q) + ?(p¯p → Z?) x ?(Z → q¯q) is calculated to be 54 pb, which is consistent with the Standard Model prediction of 20.5 pb.

Search for W' Decaying to Tau Lepton and Neutrino in Proton-proton Collisions at $\sqrt{s}$

Search for W' Decaying to Tau Lepton and Neutrino in Proton-proton Collisions at $\sqrt{s}$
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Total Pages: 21
Release: 2016
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ISBN:

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We found that the first search for a heavy charged vector boson in the final state with a tau lepton and a neutrino is reported, using 19.7 fb-1 of LHC data at √s = 8 TeV. A signal would appear as an excess of events in kinematic regions where the standard model background is low. No excess is observed. Limits are set on a model in which the W' decays preferentially to fermions of the third generation. Our results substantially extend previous constraints on this model. Masses below 2.0 to 2.7 TeV are excluded, depending on the model parameters. In addition, the existence of a W' boson with universal fermion couplings is excluded at 95% confidence level, for W' masses below 2.7 TeV.

Search for Type-III Seesaw Heavy Leptons in Leptonic Final States in Pp Collisions at [square Root]s

Search for Type-III Seesaw Heavy Leptons in Leptonic Final States in Pp Collisions at [square Root]s
Author: [Study Group] ATLAS Collaboration CERN
Publisher:
Total Pages: 0
Release: 2022
Genre:
ISBN:

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Abstract: A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to 139fb−1 of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on final states with three or four electrons or muons from the possible decays of new heavy leptons via intermediate electroweak bosons. No significant deviations above the Standard Model expectation are observed; upper and lower limits on the heavy lepton production cross-section and masses are derived respectively. These results are then combined for the first time with the ones already published by ATLAS using the channel with two leptons in the final state. The observed lower limit on the mass of the type-III seesaw heavy leptons combining two, three and four lepton channels together is 910 GeV at the 95% confidence level