A Search for \(t\overline{t} \) Resonances Using Lepton-plus-jets Events in Proton-proton Collisions at \(\sqrt{s}

A Search for \(t\overline{t} \) Resonances Using Lepton-plus-jets Events in Proton-proton Collisions at \(\sqrt{s}
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Release: 2015
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A search for new particles that decay into top quark pairs is reported. The search is performed with the ATLAS experiment at the LHC using an integrated luminosity of 20.3 fb-1 of proton-proton collision data collected at a centre-of-mass energy of \(\sqrt{s}=8 \) TeV. The lepton-plus-jets final state is used, where the top pair decays to \({W}^{+}b{W}^{-}\overline{b} \), with one W boson decaying leptonically and the other hadronically. The invariant mass spectrum of top quark pairs is examined for local excesses or deficits that are inconsistent with the Standard Model predictions. No evidence for a top quark pair resonance is found, and 95% confidence-level limits on the production rate are determined for massive states in benchmark models. The upper limits on the cross-section times branching ratio of a narrow Z' boson decaying to top pairs range from 4.2 pb to 0.03 pb for resonance masses from 0.4 TeV to 3.0 TeV. A narrow leptophobic topcolour Z' boson with mass below 1.8 TeV is excluded. Upper limits are set on the cross-section times branching ratio for a broad colour-octet resonance with [Gamma]/m = 15% decaying to \(t\overline{t} \). These range from 4.8 pb to 0.03 pb for masses from 0.4 TeV to 3.0 TeV. A Kaluza-Klein excitation of the gluon in a Randall-Sundrum model is excluded for masses below 2.2 TeV.

Search for $\mathrm{ T \bar{t} }$ Resonances in Highly-boosted Lepton+jets and Fully Hadronic Final States in Proton-proton Collisions at $ \sqrt{s}

Search for $\mathrm{ T \bar{t} }$ Resonances in Highly-boosted Lepton+jets and Fully Hadronic Final States in Proton-proton Collisions at $ \sqrt{s}
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Release: 2017
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A search for the production of heavy resonances decaying into top quark-antiquark pairs is presented. The analysis is performed in the lepton+jets and fully hadronic channels using data collected in proton-proton collisions at $\sqrt{s}$ =13 TeV using the CMS detector at the LHC, corresponding to an integrated luminosity of 2.6 inverse femtobarns. The selection is optimized for massive resonances, where the top quarks have large Lorentz boosts. No evidence for resonant ttbar production is found in the data, and upper limits on the production cross section of heavy resonances are set. The exclusion limits for resonances with masses above 2 TeV are significantly improved compared to those of previous analyses at $\sqrt{s}$ = 8 TeV.

A Search for Tt Resonances in the Single Lepton Final State with the ATLAS Experiment

A Search for Tt Resonances in the Single Lepton Final State with the ATLAS Experiment
Author: Andrew David Altheimer
Publisher:
Total Pages:
Release: 2014
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A search for undiscovered particles decaying into top-antitop quark pairs produced in proton-proton collisions with the ATLAS experiment at the Large Hadron Collider utilizing 20.3 fb$^-1$ of data collected at $\sqrt{s}=8$ \tev\ center-of-mass energy during the 2012 data taking period is presented. The invariant mass spectrum of events containing multiple jets, exactly one lepton, and missing transverse energy and which are consistent with the decay of a top-antitop quark pair is studied and found to be consistent with that predicted by the Standard Model. Upper limits on the production cross section times branching ratio of several benchmark signal models are set at a 95\% confidence level.

Searches for Dijet Resonances

Searches for Dijet Resonances
Author: Lydia Audrey Beresford
Publisher: Springer
Total Pages: 175
Release: 2018-09-04
Genre: Science
ISBN: 331997520X

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This book addresses one of the most intriguing mysteries of our universe: the nature of dark matter. The results presented here mark a significant and substantial contribution to the search for new physics, in particular for new particles that couple to dark matter. The first analysis presented is a search for heavy new particles that decay into pairs of hadronic jets (dijets). This pioneering analysis explores unprecedented dijet invariant masses, reaching nearly 7 TeV, and sets constraints on several important new physics models. The two subsequent analyses focus on the difficult low dijet mass region, down to 200 GeV, and employ a novel technique to efficiently gather low-mass dijet events. The results of these analyses transcend the long-standing constraints on dark matter mediator particles set by several existing experiments.

Searches for Light- and Heavy-flavor Three-jet Resonances in Proton-proton Collisions with the CMS Detector at $\sqrt{s}$

Searches for Light- and Heavy-flavor Three-jet Resonances in Proton-proton Collisions with the CMS Detector at $\sqrt{s}$
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Total Pages: 173
Release: 2014
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A search for three-jet hadronic resonance production in proton-proton collisions at 8 TeV center-of-mass energy has been conducted by the CMS Collaboration at the LHC. The data set corresponds to an integrated luminosity of 19.4 fb-1. The search method is modelindependent. Events are selected that contain a large number of jets with high transverse momentum. An ensemble of jets is used to extract a new possible signal from copious QCD background. Event selection is optimized using a benchmark model where supersymmetric gluinos are pair-produced and each of the gluinos decays exclusively into three jets. Two scenarios of this decay are considered denoted by the RPV couplings [lambda]'' 112 and [lambda]'' 113 or [lambda]'' 223. The first coupling allows for gluinos to decay into only light-flavor jets, while the latter two allow decays into one heavy-flavor and two light-flavor jets. No significant deviation is found between the selected events and the expected standard model multijet and t$\bar{t}$ background. For gluinos decaying through 00 112, masses below 650 GeV are excluded at the 95% confidence level. The search including heavy-flavor jets in the final state with the couplings [lambda]'' 113 or [lambda]'' 223 is the first of its kind. Gluinos decaying into one heavy-flavor and two light-flavor jets are excluded for masses between 200 and 835 GeV.

Search for New Resonances Decaying Via WZ to Leptons in Proton{u2013}proton Collisions at $\sqrt S

Search for New Resonances Decaying Via WZ to Leptons in Proton{u2013}proton Collisions at $\sqrt S
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Total Pages: 22
Release: 2014
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A search is performed in proton–proton collisions at √s=8 TeV for exotic particles decaying via WZ to fully leptonic final states with electrons, muons, and neutrinos. The data set corresponds to an integrated luminosity of 19.5 fb-1. No significant excess is observed above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of a W' boson as predicted by an extended gauge model, and on the W'WZ coupling. The expected and observed mass limits for a W' boson, as predicted by this model, are 1.55 and 1.47 TeV, respectively. Stringent limits are also set in the context of low-scale technicolor models under a range of assumptions for the model parameters.

Search for a Dijet Resonance in Events with Jets and Missing Transverse Energy in Pp[over ̄] Collisions at Sqrt[s]

Search for a Dijet Resonance in Events with Jets and Missing Transverse Energy in Pp[over ̄] Collisions at Sqrt[s]
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Release: 2013
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We report on a search for a dijet resonance in events with only two or three jets and large imbalance in the total event transverse momentum. This search is sensitive to the possible production of a new particle in association with a W or Z boson, where the boson decays leptonically with one or more neutrinos in the final state. We use the full data set collected by the CDF II detector at the Tevatron collider at a proton-antiproton center-of-mass energy of 1.96 TeV. These data correspond to an integrated luminosity of 9.1 fb{̂-1}. We study the invariant mass distribution of the two jets with highest transverse energy. We find good agreement between data and standard model background expectations and measure the combined cross section for WW, WZ, and ZZ production to be 13.8{̂+3.0}_{-2.7} pb. No significant anomalies are observed in the mass spectrum and 95% credibility level upper limits are set on the production rates of a potential new particle in association with a W or Z boson.

Search for Pair-produced Resonances Decaying to Jet Pairs in Proton{u2013}proton Collisions at $\sqrt{s}$

Search for Pair-produced Resonances Decaying to Jet Pairs in Proton{u2013}proton Collisions at $\sqrt{s}$
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Total Pages: 22
Release: 2015
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Results are reported of a general search for pair production of heavy resonances decaying to pairs of hadronic jets in events with at least four jets. The study is based on up to 19.4 fb–1 of integrated luminosity from proton–proton collisions at a center-of-mass energy of 8 TeV, recorded with the CMS detector at the LHC. Limits are determined on the production of scalar top quarks (top squarks) in the framework of R-parity violating supersymmetry and on the production of color-octet vector bosons (colorons). First limits at the LHC are placed on top squark production for two scenarios. The first assumes decay to a bottom quark and a light-flavor quark and is excluded for masses between 200 and 385 GeV, and the second assumes decay to a pair of light-flavor quarks and is excluded for masses between 200 and 350 GeV at 95% confidence level. Furthermore, previous limits on colorons decaying to light-flavor quarks are extended to exclude masses from 200 to 835 GeV.