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The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
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Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Searching for Vector-Like Quarks Using 36.1 fb^{-1} Of Proton-Proton Collisions Decaying to Same-Charge Dileptons and Trileptons + b-jets at √s = 13 TeV with The ATLAS DetectorJones, Sarah, Jones, Sarah January 2017 (has links)
Since the discovery of the Higgs boson in 2012, the search for new physics beyond
the Standard Model has been greatly intensified. At the CERN Large Hadron Collider
(LHC), ATLAS searches for new physics entail looking for new particles by colliding
protons together. Presented here is a search for a new form of quark matter called
Vector-like Quarks (VLQ), which are hypothetical particles that are expected to have
mass around a few TeV. VLQ can come in a variety of forms and can couple to
their Standard Model (SM) quark counterparts, particularly to the third generation.
They are necessary in several beyond the SM theories in order to solve the hierarchy
problem. This search uses 36.1 fb−1of proton-proton collision data collected with the
ATLAS detector at the LHC from August 2015 to October 2016. Only events with two
leptons of the same charge, or three leptons, plus b-jets and high missing transverse
energy are considered in the main analysis. This signature is rarely produced in the
SM, which means the backgrounds in this analysis are relatively low. This analysis
is sensitive to specific predicted decay modes from pair production of an up-type
VLQ with a charge of +2/3, T, an up-type VLQ with a charge of +5/3, T5/3, and
a down-type quark with a charge of −1/3, B, as well as single production of T5/3.
There is another theorized VLQ that this analysis is not sensitive to: B−4/3, due
to its primary decay mode, which is unable to produce the final-state signature of
interest. The results from this analysis suggest only a slight deviation of data from
SM backgrounds reaching as high as 1.89σ, which does not indicate evidence for
VLQ. A mostly frequentist statistical technique, called the CLS Method, is used to
interpret the data and set limits on the T, B, and T5/3 signal models. Using this
method, exclusion limits are set at the 95% confidence level, effectively excluding T
mass below 0.98 TeV, T5/3 mass below 1.2 TeV, and B mass below 1.0 TeV, assuming
singlet branching ratios. Also, branching ratio independent limits are set on the T
and B VLQ.
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Searches for dijet resonances using √s = 13 TeV proton-proton collision data recorded by the ATLAS detector at the Large Hadron ColliderBeresford, Lydia Audrey January 2017 (has links)
This thesis presents three searches for new resonances in dijet invariant mass spectra. The spectra are produced using √s = 13 TeV proton-proton collision data recorded by the ATLAS detector. New dijet resonances are searched for in the mass range 200 GeV to 6.9 TeV in mass. Heavy new resonances, with masses above 1.1 TeV, are targeted by a high mass dijet search. Light new resonances, with masses down to 200 GeV, are searched for in dijet events with an associated high momentum object (a photon or a jet) arising from initial state radiation. The associated object is used to efficiently trigger the recording of low mass dijet events. All of the analyses presented in this thesis search for an excess of events, localised in mass, above a data-derived estimate of the smoothly falling QCD background. In each search no evidence for new resonances is observed, and the data are used to set 95% C.L. limits on the production cross-section times acceptance times branching ratio for model-independent Gaussian resonance shapes, as well as benchmark signals. One particular benchmark signal which is considered in all of the searches is an axial-vector Z' dark matter mediator model whose parameter space is reduced due to the results presented in this thesis.
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Measurement of Higgs boson properties using the decay channel to b-quarks following associated production with a vector boson in pp collisions at √s=13 TeV / 重心系エネルギー13 TeVの陽子陽子衝突におけるヒッグス粒子のbクォークへの崩壊とベクトルボソン随伴生成を使用したヒッグス粒子の性質測定Noguchi, Yohei 23 March 2021 (has links)
京都大学 / 新制・課程博士 / 博士(理学) / 甲第22999号 / 理博第4676号 / 新制||理||1671(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査) 長野 邦浩, 教授 中家 剛, 准教授 吉岡 興一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM
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Exotic Decays of a Vector-liketop Partner at the LHCSkwarcan-Bidakowski, Alexander January 2019 (has links)
An evaluation of how sensitive some ATLAS searches for new physics are to a new beyond standard model (BSM) vector-like quark (VLQ) and a pseudo Nambu-Goldstone boson (pNGB) scalar. This was done by simulating a signal containing these new particles and making a recast of it onto existing verified ATLAS searches for new physics at center-of-mass (CM) energy of 13 TeV (Run 2) at the Large Hadron Collider (LHC). Signals for recasting were tailored such that their final states would be appropriate in relation to each respective ATLAS search in order to use the same selection criteria as applied in the existing searches. The results are summarized in the form of significances (Z) for each masspoint of the new top-partner and S particle. Significances did not show any expectiation of excluding any masspoint in the examined mass range for the recasts at 95% CL. This suggests that a dedicated search for these particles in the considered masspoints would be required.
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