Search for Charged Higgs Bosons Decaying Via H± → Τ±ν in Fully Hadronic Final States with the ATLAS Detector at the LHC
Search for Charged Higgs Bosons Decaying Via H± → Τ±ν in Fully Hadronic Final States with the ATLAS Detector at the LHC

Author: Anna Kopp

Publisher:

Published: 2015

Total Pages:

ISBN-13:

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Zusammenfassung: Searches for charged Higgs bosons decaying to a tau lepton and a neutrino in fully hadronic final states are presented in this thesis. The analyses are based on 4.6fb^-1 and 19.5fb^-1 of proton-proton collision data taken with the ATLAS detector at the LHC at center-of-mass energies of 7TeV and 8TeV in 2011 and 2012, respectively.Charged Higgs bosons with masses less than the top quark mass are searched for in events consistent with top-quark pair production and charged Higgs bosons with masses greater than the top quark mass are searched for in associated production with a top quark.In the search based on data taken in 2011, all background contributions are estimated in data-driven ways. Only a minor background contribution is estimated using simulation in the searches based on data taken in 2012; all dominant background contributions are estimated using data-driven methods here as well. An embedding method is used in all searches to assess the dominant and irreducible background contributions containing true hadronically decaying tau leptons and described in detail in this thesis.No significant excess of the data compared to the background expectations due to Standard Model processes is observed. Statistical analyses lead to 95% confidence-level upper limits on the branching ratios B(t->bH^±)xB(H^±->tau^± nu) between 0.23% and 1.3% for charged Higgs boson masses between 80GeV and 160GeV and on the production cross section times branching ratio, sigma(pp->tH^±+X)xB(H^±->tau^± nu) ranging from 0.76pb to 4.5fb for charged Higgs boson masses between 180GeV and 1000GeV. The branching ratio and cross section limits are used to derive constraints on the parameter space of minimal supersymmetric extensions of the Standard Model in various benchmark scenarios. These limits are the so far strictest limits set by the ATLAS collaboration in the search for charged Higgs bosons in fully hadronic final states

Searches for the Exclusive Higgs and the Charged Higgs Bosons with the ATLAS Detector at the LHC
Searches for the Exclusive Higgs and the Charged Higgs Bosons with the ATLAS Detector at the LHC

Author: Last Feremenga

Publisher:

Published: 2017

Total Pages: 247

ISBN-13:

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In this thesis, searches for the exclusive Standard Model (SM) and charged hMSSM Higgs bosons are performed. While observations of the SM Higgs boson in 2012 by ATLAS and CMS collaborations were ground-breaking, several of the SM Higgs boson properties such as its coupling strengths and branching ratios of its decays still carry large systematic uncertainties. Higgs boson candidates from exclusive production could lower these systematic uncertainties due to their cleaner production environment, improving knowledge of the SM Higgs boson sector. Since the charged Higgs boson is not included in the SM, its evidence would clearly indicate physics beyond the SM which could address the hierarchy problem. Since no signal is observed for either of these bosons, limits to their production cross sections are set. A 95% confidence-level upper limit on the total production cross-section for exclusive Higgs boson is set to 1.2 pb. Limits on the total production cross section of the charged Higgs boson times its branching ratio to [T V] are set between 1.9 pb and 15 fb, for charged Higgs boson masses ranging from 200 to 2000 GeV.

Search for Charged Higgs Bosons in Tau-lepton Final States with 139 Inverse Femtobarns of Proton-proton Collision Data Recorded at a Centre of Mass Energy of 13 TeV with the ATLAS Detector
Search for Charged Higgs Bosons in Tau-lepton Final States with 139 Inverse Femtobarns of Proton-proton Collision Data Recorded at a Centre of Mass Energy of 13 TeV with the ATLAS Detector

Author: Sina Bahrasemani

Publisher:

Published: 2019

Total Pages: 240

ISBN-13:

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The Higgs boson, with a measured mass of approximately $125~GeV$, has been studied extensively since its discovery in 2012 at the Large Hadron Collider. This discovery opens the question of whether the Higgs boson of the Standard Model (SM) is the only scalar particle of Nature or it belongs to a larger scalar sector, as predicted in many Beyond the Standard Model (BSM) theories. Therefore, observation of charged Higgs bosons would indicate new physics. This thesis presents results of a search for a charged Higgs boson in the mass range $80~GeV$ to $3~TeV$, through tau-lepton final states. The search is performed using proton-proton collisions data at $\sqrt{s}=13~\mbox{TeV}$, collected with the ATLAS experiment, during 2015 to 2018. The final results are interpreted in the context of the Minimal SuperSymmetric Standard Model (MSSM) benchmark scenarios. In these scenarios, charged Higgs bosons coupling to tau-lepton are enhanced for some parts of the search phase space, thus increasing the chance of their discovery. No significant excess of events above the expected background from the Standard Model processes is observed. Therefore, upper limits on the charged Higgs boson production cross section times its branching ratio to tau-lepton and its associated neutrino are set at a 95\% Confidence Level. The results are also interpreted in the context of the hMSSM and $m^{mod -}_{h}$ benchmark scenarios of the MSSM. Due to the enhancement of the charged Higgs boson coupling to tau-leptons at high values of the $\tan\beta$ parameter of the MSSM, it is possible to exclude the high $\tan\beta$ region in the $M_{H^{\pm}}$--$\tan\beta$ parameter space. In this work, $\tan\beta$ values around 60 are excluded up to a charged Higgs boson mass of $1400~\GeV$. Furthermore, in the low mass region, below $170~GeV$, all values of $\tan\beta$ in range 1--60 are excluded at 95\% confidence level.

Search for the Higgs Boson in the Vector Boson Fusion Channel at the ATLAS Detector
Search for the Higgs Boson in the Vector Boson Fusion Channel at the ATLAS Detector

Author: Eric Ouellette

Publisher: Springer

Published: 2015-01-20

Total Pages: 114

ISBN-13: 3319135996

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This Thesis describes the first measurement of, and constraints on, Higgs boson production in the vector boson fusion mode, where the Higgs decays to b quarks (the most common decay channel), at the LHC. The vector boson fusion mode, in which the Higgs is produced simultaneously with a pair of quark jets, provides an unparalleled opportunity to study the detailed properties of the Higgs, including the possibility of parity and CP violation, as well as its couplings and mass. It thus opens up this new field of study for precision investigation as the LHC increases in energy and intensity, leading the way to this new and exciting arena of precision Higgs research.