Searches for Top-antitop Resonances in Proton-proton Collisions at a Center of Mass Energy of 7 TeV with the ATLAS Detector PDF Download
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Author: Jean-Raphael Lessard
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Languages : en
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The LHC and the ATLAS detector offer an unprecedented opportunity to test theories beyond the Standard Model of particle physics. Some of these theories predict heavy particles that would decay predominantly into a top and an antitop quark. This thesis presents a technique to experimentally measure the invariant mass (Mtt) of top-antitop pairs, event-by-event, allowing for a complete reconstruction of the Mtt spectrum. Two different models of heavy narrow resonances were considered: a particle X with a negligible mass width, and a Z' particle. Under these models, no resonances in the Mtt spectrum were found in 35.3 pb-1 of 7 TeV centre of mass proton-proton collision data. An upper limit on the production cross section times the branching ratio of the heavy particle decaying into a top-antitop (Sup) as a function of its mass (Mx or Mz) was established at a 95% confidence level. Including systematic errors, the observed (expected) Sup at 95% varies from 3.2 pb (27.9 +11.3 -19.9 pb) to 77.7 pb (9.8 +10.7 -5.6 pb) for Mx ranging from 760 GeV to 1000 GeV, and from 2.9 pb (55.9 +56.9 -47.0 pb) to 43.4 pb (7.8 +8.9 -4.7 pb) for Mz ranging from 700 GeV to 1000 GeV.
Author: Jean-Raphael Lessard
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ISBN:
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Languages : en
Pages :
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Book Description
The LHC and the ATLAS detector offer an unprecedented opportunity to test theories beyond the Standard Model of particle physics. Some of these theories predict heavy particles that would decay predominantly into a top and an antitop quark. This thesis presents a technique to experimentally measure the invariant mass (Mtt) of top-antitop pairs, event-by-event, allowing for a complete reconstruction of the Mtt spectrum. Two different models of heavy narrow resonances were considered: a particle X with a negligible mass width, and a Z' particle. Under these models, no resonances in the Mtt spectrum were found in 35.3 pb-1 of 7 TeV centre of mass proton-proton collision data. An upper limit on the production cross section times the branching ratio of the heavy particle decaying into a top-antitop (Sup) as a function of its mass (Mx or Mz) was established at a 95% confidence level. Including systematic errors, the observed (expected) Sup at 95% varies from 3.2 pb (27.9 +11.3 -19.9 pb) to 77.7 pb (9.8 +10.7 -5.6 pb) for Mx ranging from 760 GeV to 1000 GeV, and from 2.9 pb (55.9 +56.9 -47.0 pb) to 43.4 pb (7.8 +8.9 -4.7 pb) for Mz ranging from 700 GeV to 1000 GeV.
Author: Bertrand Chapleau
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Languages : en
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"The intriguing nature of the top quark, by far the heaviest particle in the Standard Model of particle physics, has motivated the development of many theoretical extensions predicting the existence of new massive particles decaying to a pair of top-antitop quarks. The production of these hypothetical particles in proton-proton collisions at the Large Hadron Collider would reveal itself as a resonance in the expected smooth distribution of the top-antitop quark invariant mass. This thesis presents a search for such a new heavy particle decaying to a pair of top-antitop quarks in the semi-leptonic final state. The analyzed data sample amounts to a total of 4.6 fb-1 at a proton-proton collision center-of-mass energy of 7 TeV. Novel techniques specifically tailored to the identification of the decay products of highly energetic top quarks are developed and used. No evidence for resonant production of pairs of top-antitop quarks is found and, as a result, constraints are set on two theoretical models. Upper limits on the production cross-section times branching ratio are established at a 95% credibility level for a leptophobic Zʹ boson from the Topcolor model, and a Kaluza-Klein gluon from the Randall-Sundrum model. The Zʹ boson and the Kaluza-Klein gluon are excluded to exist (at a 95% credibility level) in the mass ranges 0.8-1.65 TeV and 0.8-1.88 TeV, respectively. The constraints de- rived in this thesis on the two theoretical models are more stringent than the ones obtained at other experiments, thanks to the large center-of-mass energy and the dedicated high-energy top quark identification techniques used." --
Author: Christian Göringer
Publisher:
ISBN:
Category :
Languages : en
Pages : 180
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Author: Andrew David Altheimer
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Category :
Languages : en
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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.
Author: Christian Göringer
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Languages : en
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Author: Kiran Joshi
Publisher: Springer
ISBN: 3319196537
Category : Science
Languages : en
Pages : 188
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Book Description
This thesis contains new research in both experimental and theoretical particle physics, making important contributions in each. Two analyses of collision data from the ATLAS experiment at the LHC are presented, as well as two phenomenological studies of heavy coloured resonances that could be produced at the LHC. The first data analysis was the measurement of top quark-antiquark production with a veto on additional jet activity. As the first detector-corrected measurement of jet activity in top-antitop events it played an important role in constraining the theoretical modelling, and ultimately reduced these uncertainties for ATLAS's other top-quark measurements by a factor of two. The second data analysis was the measurement of Z+2jet production and the observation of the electroweak vector boson fusion (VBF) component. As the first observation of VBF at a hadron collider, this measurement demonstrated new techniques to reliably extract VBF processes and paved the way for future VBF Higgs measurements. The first phenomenological study developed a new technique for identifying the colour of heavy resonances produced in proton-proton collisions. As a by-product of this study an unexpected and previously unnoticed correlation was discovered between the probability of correctly identifying a high-energy top and the colour structure of the event it was produced in. The second phenomenological study explored this relationship in more detail, and could have important consequences for the identification of new particles that decay to top quarks.
Author: Daiki Yamaguchi
Publisher: Springer Nature
ISBN: 9811509328
Category : Science
Languages : en
Pages : 279
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Book Description
This book reports on the search for a new heavy particle, the Vector-Like Top quark (VLT), in the Large Hadron Collider (LHC) at CERN. The signal process is the pair production of VLT decaying into a Higgs boson and top quark (TT→Ht+X, X=Ht, Wb, Zt). The signal events result in top–antitop quarks final states with additional heavy flavour jets. The book summarises the analysis of the data collected with the ATLAS detector in 2015 and 2016. In order to better differentiate between signals and backgrounds, exclusive taggers of top quark and Higgs boson were developed and optimised for VLT signals. These efforts improved the sensitivity by roughly 30%, compared to the previous analysis. The analysis outcomes yield the strongest constraints on parameter space in various BSM theoretical models. In addition, the book addresses detector operation and the evaluation of tracking performance. These efforts are essential to properly collecting dense events and improving the accuracy of the reconstructed objects that are used for particle identification. As such, they represent a valuable contribution to data analysis in extremely dense environments.
![Measurement of the Z → _t63_1hn+_t63_1hn- [Z → Tau + Tau -] Production Cross Section in Proton-proton Collisions at 7 TeV Center-of-mass Energy with the ATLAS Detector PDF](https://books.google.com/books/content/images/frontcover/pNsxnwEACAAJ?fife=w80-h100)
Author: Daniele Capriotti
Publisher:
ISBN:
Category :
Languages : en
Pages : 113
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![Search for Pair-produced Resonances Decaying to Jet Pairs in Proton-proton Collisions at [arrow]](https://books.google.com/books/content/images/frontcover/zDQ2nQAACAAJ?fife=w80-h100)
Author:
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Category :
Languages : en
Pages : 31
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Book Description
Results are reported of a general search for pair production of heavy resonances decaying to pairs of jets in events with at least four jets. The study is based on up to 19.4 inverse femtobarns 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. Previous limits on colorons decaying to light-flavor quarks are extended to exclude masses from 200 to 835 GeV.
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Languages : en
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Book Description
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.
