79 research outputs found
ATLAS Thesis Awards 2015
No full textWinners of the ATLAS Thesis Award were presented with certificates and glass cubes during a ceremony on Thursday 25 February. The winners also presented their work in front of members of the ATLAS Collaboration. Winners: Javier Montejo Berlingen, Barcelona (Spain), Ruth Pöttgen, Mainz (Germany), Nils Ruthmann, Freiburg (Germany), and Steven Schramm, Toronto (Canada)
Physics with Tau-Lepton Final States in ATLAS
No full textHeading into its third year of data-taking ATLAS already published a large number of measurements and searches for processes with leptons in the final state. In this note a broad overview over the ATLAS physics programme involving -leptons will be given. Searches for a SM Higgs boson, charged Higgs bosons as proposed in supersymmetric models and searches for supersymmetry in events with tau leptons are presented as well as Standard Model measurements. The first measurement of the polarization in decays at a hadron collider and the challenging measurement of the cross-section in the final state are discussed. All observations agree well with the SM prediction
Datenbasierte Abschätzung der Energieskala hadronisch zerfallender Tau-Leptonen zur Steigerung der Sensitivität einer Higgs-Analyse im Kanal qq-->qqH-->qqtautau-->qq lnu hnu mit dem ATLAS Detektor
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Search for Standard Model Decays in the Lepton-Hadron Final State in Proton-Proton Collisions with the ATLAS Detector at the LHC
No full textThis thesis presents a search for Standard Model (SM) Higgs boson decays to a pair of tau leptons in the lepton-hadron final state with the ATLAS detector at the Large Hadron Collider (LHC). The analysis is based on proton-proton collision data recorded during Run 1 of the LHC, corresponding to integrated luminosities of 4.5 fb and 20.3 fb at centre-of-mass energies of 7 TeV and 8 TeV, respectively. Background events from various SM processes contribute to the selected event sample at a high rate. Their contribution is efficiently separated from the expected Higgs boson signal by using boosted decision trees (BDT) in two analysis categories, which are enriched in events emerging from vector boson fusion and gluon fusion processes. The expected number of events from background processes is modelled using data-driven estimation techniques. The signal contribution is measured using a maximum likelihood fit of the BDT output distributions. An excess of events over the expected level of background events is found and corresponds to an observed (expected) significance of 2.3 (2.4) standard deviations at a Higgs boson mass hypothesis of 125 GeV. The signal strength normalised to the Standard Model expectation is measured to be . A combined analysis of all tau-tau final states rejects the background-only hypothesis at a level of 4.5 standard deviations at GeV, while a significance of 3.5 standard deviations is expected. This provides evidence for the direct coupling of the recently discovered Higgs boson to tau leptons. The measured normalised signal strength of is consistent with the predicted Yukawa coupling strength in the Standard Model
Suche nach Standardmodell H->tau^+tau^- Zerfällen im Lepton-Hadron Endzustand in Proton-Proton Kollisionen mit dem ATLAS Detektor am LHC
No full textThis thesis presents a search for Standard Model (SM) Higgs boson decays to a pair of tau leptons in the lepton-hadron final state with the ATLAS detector at the Large Hadron Collider (LHC).
The analysis is based on proton-proton collision data recorded during Run 1 of the LHC, corresponding to integrated luminosities of 4.5 fb^-1 and 20.3 fb^-1 at centre-of-mass energies of 7 TeV and 8 TeV, respectively.
Background events from various SM processes contribute to the selected event sample at a high rate.
Their contribution is efficiently separated from the expected Higgs boson signal by using boosted decision trees (BDT) in two analysis categories, which are enriched in events emerging from vector boson fusion and gluon fusion processes.
The expected number of events from background processes is modelled using data-driven estimation techniques.
The signal contribution is measured using a maximum likelihood fit of the BDT output distributions.
An excess of events over the expected level of background events is found and corresponds to an observed (expected) significance of 2.3 (2.4) standard deviations at a Higgs boson mass hypothesis of 125 GeV. The signal strength normalised to the Standard Model expectation is measured to be 0.98+0.5-0.5.
A combined analysis of all tau-tau final states rejects the background-only hypothesis at a level of 4.5 standard deviations at m_H=125 GeV, while a significance of 3.5 standard deviations is expected.
This provides evidence for the direct coupling of the recently discovered Higgs boson to tau leptons.
The measured normalised signal strength of 1.4+0.43-0.37 is consistent with the predicted Yukawa coupling strength in the Standard Model.
Die vorliegende Dissertation stellt eine Suche nach Standardmodell (SM) Higgs Boson Zerfällen in ein Tau-Leptonen-Paar im Lepton-Hadron Endzustand vor. Die Analyse basiert auf einem Datensatz von Proton-Proton Kollisionen von 4.5 fb^-1 und 20.3 fb^-1 bei Schwerpunktsenergien von 7 bzw. 8 TeV, aufgenommen vom ATLAS Detektor am Large-Hadron-Collider (LHC).
Untergrundereignisse aus verschiedensten SM Prozessen tragen den größten Anteil zum selektierten Ereignissample bei.
Um diese Ereignisse effizient von den erwarteten Higgs Boson Signalereignissen zu trennen, werden Boosted Decision Trees (BDT) in zwei Ereignisskategorien verwendet, welche in Ereignissen aus Vektor Boson Fusion und Gluon Fusions Prozessen angereichert sind.
Die Untergrunderwartung wird mittels datenbasierter Methoden abgeschätzt und der Beitrag von Higgs Boson Signalereignissen in einem Maximum Likelihood Fit der BDT Verteilungen gemessen.
Ein Überschuss von Ereignissen über dem erwarteten Untergrund mit einer statistischen Signifikanz von 2.3 Standardabweichungen bei einer Higgs Boson Massenhypothese von m_H=125 GeV wird beobachtet. Die auf die Standardmodell Erwartung normierte Signalstärke beträgt 0.98+0.5-0.5.
In einer kombinierten Analyse aller Tau-Tau Endzustände kann die Untergrundhypothese mit einer Signifikanz von 4.5 Standardabweichungen ausgeschlossen werden, bei einer erwarteten Signifikanz von 3.5 Standardabweichungen.
Dies stellt eine Evidenz für die direkte Kopplung des kürzlich entdeckten Higgs Bosons an Tau Leptonen dar.
Die gemessene relative Signalstärke ist 1.4+0.43-0.37 und damit in guter Übereinstimmung mit der Yukawa Kopplungsstärke im Standardmodell
SM Higgs Couplings
No full textOverview over the status of SM Higgs Boson couplings after LHC Run 1. Summarizing the results of the ATLAS+CMS combination. Talk to be given at PIC2015
Measurements of the Coupling Properties of the Standard Model Higgs Boson
No full textOverview over the status of SM Higgs Boson couplings after LHC Run 1. Summarizing the results of the ATLAS+CMS combination. Proceedings to a talk given at PIC2015
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