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Signatures of vector-like top partners decaying into new neutral scalar or pseudoscalar bosons
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.ORCID iD: 0000-0002-1253-8583
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
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2019 (English)In: Article in journal (Other academic) Epub ahead of print
Abstract [en]

We explore the phenomenology of models containing one Vector-Like Quark (VLQ), t′, which can decay into the Standard Model (SM) top quark, t, and a new spin-0 neutral boson, S, the latter being either a scalar or pseudoscalar state. We parametrise the underlying interactions in terms of a simplified model which enables us to capture possible Beyond the SM (BSM) scenarios. We discuss in particular three such scenarios: one where the SM state is supplemented by an additional scalar, one which builds upon a 2-Higgs Doublet Model (2HDM) framework and another which realises a Composite Higgs Model (CHM) through partial compositeness. Such exotic decays of the t′ can be competitive with decays into SM particles, leading to new possible discovery channels at the Large Hadron Collider (LHC). Assuming t′ pair production via strong interactions, we design signal regions optimised for one t′→St transition (while being inclusive on the other \bar{t'} decay, and vice versa), followed by the decay of S into the two very clean experimental signatures S→γγ and S→Z(→ℓ+ℓ−)γ. We perform a dedicated signal-to-background analysis in both channels, by using Monte Carlo (MC) event simulations modelling the dynamics from the proton-proton to the detector level. Under the assumption of BR(t′→St)=100%, we are therefore able to realistically quantify the sensitivity of the LHC to both the t′ and S masses, assuming both current and foreseen luminosities. This approach paves the way for the LHC experiments to surpass current VLQ search strategies based solely on t′ decays into SM bosons (W±,Z, h).

Place, publisher, year, edition, pages
2019.
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:uu:diva-389895OAI: oai:DiVA.org:uu-389895DiVA, id: diva2:1339732
Available from: 2019-07-31 Created: 2019-07-31 Last updated: 2019-08-15Bibliographically approved
In thesis
1. Exploration of extended Higgs sectors, development of a displaced track trigger, and improvements in GRID middleware
Open this publication in new window or tab >>Exploration of extended Higgs sectors, development of a displaced track trigger, and improvements in GRID middleware
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Two possible solutions to the Standard Model (SM) fine-tuning problem are presented in this thesis, MSSM and Compositeness. The Higgs sector of the MSSM can be tested by searching for charged Higgs bosons. Two direct searches for charged Higgs bosons decaying into a top- and bottom-quark are performed using 13.2 and 36.1 fb¹ respectively of pp collision data collected at √s = 13 TeV with the ATLAS detector. No significant excess over the SM background is observed and upper limits on σ(pp→tbH+B(H+→tb) between 0.07 and 2.9 pb are set at a 95% confidence level in the charged Higgs boson mass range 200–2000 GeV using the CLs method. The phenomenology of a vector-like top-partner decaying into a BSM (pseudo-) scalar is explored and interpreted in 2HDM and Compositeness models. The experimental reach is evaluated using γγ and Zγ final states, and the LHC is determined to be sensitive to top-partner and (pseudo-) scalar masses in the 1–2 TeV range both in the Run 2 and expected Run 3 datasets. Two hardware based hit collection methods targeting long-lived particles are studied for a regional track trigger in anticipation of the HL-LHC upgrade. The efficiency is estimated to be ~20% for a wide range of track parameters for tracks originating from a displaced vertex. The prospect of using GPU-computing on the LHC GRID is considered. Extensions of the ARC middleware Information Providers integrating local GPU information are demonstrated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 95
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1829
Keywords
BSM, Supersymmetry, Standard Model, Higgs, 2HDM, Charged Higgs, Compositeness, Pattern Matching, GRID
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-389896 (URN)978-91-513-0700-8 (ISBN)
Public defence
2019-09-20, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2019-08-28 Created: 2019-07-31 Last updated: 2019-09-17

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Bergeås Kuutmann, ElinEllajosyula, VenugopalEnberg, RikardIsacson, MaxMandal, TanumoyMathisen, ThomasPanizzi, Luca

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