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Embedding Technique for the ttbar Background Estimation in Charged Higgs Boson Searches
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Nuclear and Particle Physics, High Energy Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Nuclear and Particle Physics, High Energy Physics.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Standard Model-like decays of a top quark pair with tau leptons are the dominant background for most charged Higgs boson searches. It is shown that the background can be emulated starting from a pure ttbar->bmunu bW sample by replacing tracks and calorimeter cells on an ESD (Event Summary Data) level in close vicinity to the muon with those of a simulated tau lepton. ATLAS reconstruction algorithms are then re-run to provide higher-level objects, eliminating the need of ad-hoc corrections to the missing energy. Relevant distributions like top quark invariant masses, tau jet properties and missing transverse energy can be reproduced within a 10% level.

Keyword [en]
ATLAS Embedding Charged Higgs ttbar tau
URN: urn:nbn:se:uu:diva-110771OAI: oai:DiVA.org:uu-110771DiVA: diva2:278222
Available from: 2009-11-24 Created: 2009-11-24 Last updated: 2012-10-10
In thesis
1. Looking for the Charged Higgs Boson: Simulation Studies for the ATLAS Experiment
Open this publication in new window or tab >>Looking for the Charged Higgs Boson: Simulation Studies for the ATLAS Experiment
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The discovery of a charged Higgs boson (H+) would be an unambiguous sign of physics beyond the Standard Model. This thesis describes preparations for the H+ search with the ATLAS experiment at the Large Hadron Collider at CERN. The H+ discovery potential is evaluated, and tools for H+ searches are developed and refined.

The H+→τν decay mode has been known as the most promising H+ discovery channel. Within this thesis, first studies of this channel with realistic detector simulation, trigger simulation and consideration of all dominant systematic uncertainties have been performed. Although, as shown by these studies, the discovery sensitivity is significantly degraded compared to studies using a parametrized detector simulation, this channel remains the most powerful ATLAS H+ discovery mode. Future searches will rely on multivariate analysis techniques like the Iterative Discriminant Analysis (IDA) method. First studies indicate that a significant sensitivity increase can be achieved compared to studies based on sequential cuts. The largest uncertainty in H+ searches is the expected $t\bar{t}$ background contribution. It is shown that numbers obtained from simulated events could be off by a factor of two, decreasing the discovery sensitivity dramatically. In this thesis, the Embedding Method for data-driven background estimation is presented. By replacing the muon signature in $t\bar{t}$ events with a simulated τ, events which allow an estimation of the background contribution at the 10% level are obtained.

The ATLAS τ identification focuses on comparably clean environments like Z and W decays. To optimize the performance in high-multiplicity events like H+→τν, tau leptons are studied in $t\bar{t}$ and pile-up events. Variables which do not show discrimination power in high-multiplicity events are identified, and in some cases similar, more powerful variables are found. This allows to recover some of the performance loss and to increase the robustness of the τ identification.

For the analysis of large amounts of data produced by the ATLAS detector, seamless interoperability of the various Grid flavors is required. This thesis introduces translators to overcome differences in the information system between a number of Grid projects,and highlights important areas for future standardization.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. VI+50 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 696
charged Higgs, tau, ATLAS, HEP, CERN, LHC, Particle Physics, Grid
National Category
Physical Sciences
Research subject
High Energy Physics
urn:nbn:se:uu:diva-110882 (URN)978-91-554-7676-2 (ISBN)
Public defence
2010-01-15, Polhemsalen, Ångström Laboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Available from: 2009-12-22 Created: 2009-11-30 Last updated: 2009-12-22Bibliographically approved

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