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Signatures of vector-like top partners decaying into new neutral scalar or pseudoscalar bosons
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Högenergifysik.ORCID-id: 0000-0002-1253-8583
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Högenergifysik.
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2019 (Engelska)Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479Artikel i tidskrift (Övrigt vetenskapligt) Accepted
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).

Ort, förlag, år, upplaga, sidor
2019.
Nationell ämneskategori
Subatomär fysik
Forskningsämne
Fysik med inriktning mot elementarpartikelfysik
Identifikatorer
URN: urn:nbn:se:uu:diva-389895OAI: oai:DiVA.org:uu-389895DiVA, id: diva2:1339732
Forskningsfinansiär
Knut och Alice Wallenbergs Stiftelse, KAW 2017.0100Tillgänglig från: 2019-07-31 Skapad: 2019-07-31 Senast uppdaterad: 2020-04-17
Ingår i avhandling
1. Exploration of extended Higgs sectors, development of a displaced track trigger, and improvements in GRID middleware
Öppna denna publikation i ny flik eller fönster >>Exploration of extended Higgs sectors, development of a displaced track trigger, and improvements in GRID middleware
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2019. s. 95
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1829
Nyckelord
BSM, Supersymmetry, Standard Model, Higgs, 2HDM, Charged Higgs, Compositeness, Pattern Matching, GRID
Nationell ämneskategori
Subatomär fysik
Forskningsämne
Fysik med inriktning mot elementarpartikelfysik
Identifikatorer
urn:nbn:se:uu:diva-389896 (URN)978-91-513-0700-8 (ISBN)
Disputation
2019-09-20, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2019-08-28 Skapad: 2019-07-31 Senast uppdaterad: 2020-05-13

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