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Charged Higgs Boson Searches
2008 (English)In: Expected Performance of the ATLAS Experiment: Detector, Trigger and Physics, Geneva: CERN , 2008Chapter in book (Other academic)
##### Abstract [en]

The discovery of a charged Higgs boson would be tangible proof of physics beyond the Standard Model. This note presents the ATLAS potential for discovering a charged Higgs boson, utilizing five different final states of the signal arising from the three dominating fermionic decay modes of the charged Higgs boson. The search covers the region below the top quark mass, taking into account the present experimental constraints, the transition region with a charged Higgs boson mass of the order of the top quark mass, and the high-mass region with a charged Higgs boson mass up to 600 GeV. All studies are performed with a realistic simulation of the detector response including all three trigger levels and taking into account all dominant systematic uncertainties. Results are given in terms of discovery and exclusion contours for each channel individually and for all channels combined, showing that the ATLAS experiment is capable of detecting the charged Higgs boson in a significant fraction of the (tanb, mH±) parameter space with its first 10 fb−1 of data. The so-called intermediate tanb region (around tanb = 7) is experimentally hard to reach but exclusion sensitivity is given in this area.

##### Place, publisher, year, edition, pages
Geneva: CERN , 2008.
##### Keyword [en]
ATLAS Charged Higgs Boson Searches
##### Identifiers
ISBN: 978-92-9083-321-5 (print)OAI: oai:DiVA.org:uu-110660DiVA: diva2:277890
Available from: 2009-11-21 Created: 2009-11-21 Last updated: 2011-03-04
##### In thesis
1. Charged Higgs Bosons at the ATLAS Experiment and Beyond
Open this publication in new window or tab >>Charged Higgs Bosons at the ATLAS Experiment and Beyond
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
##### Abstract [en]

In the ATLAS experiment at the Large Hadron Collider (LHC) at CERN, direct searches for the elusive Higgs boson will be conducted, as well as for physics beyond the Standard Model. The charged Higgs boson (H±) is interesting both as a part of the Higgs sector, and as a clear sign of new physics. This thesis focuses on H± searches, with H± production in top-antitop pair events, and in particular the  bW± bH±, H±→τhadν, W±→qq channel. Its potential was investigated  as  part of a larger study of the expected performance of the entire ATLAS experiment. Full simulation of the ATLAS detector and trigger was used, and all dominant systematics considered. It was shown to be the most promising H± discovery channel for m<mt.

As hadronic τ decays are important for H± searches, their correct identification is critical. Possibilities of improving tau-jet identification in  pile-up and top-antitop pair events were investigated. Redundant or even performance-reducing variables in the default likelihood identification were identified, as were new variables showing discriminatory power. This allows for increased rejection of QCD jets in these environments, and higher robustness of the method.

Before any physics studies, a commissioned and well-understood detector is required. The Lorentz angle of the ATLAS Semi-Conductor Tracker (SCT) barrel was measured using 2008 cosmic-ray data. It is an important observable for the performance of several detector aspects. Potential sources of systematics were investigated and evaluated. The Lorentz angle in the SCT barrel was measured as θL = 3.93 ± 0.03(stat) ± 0.10(syst) degrees, agreeing with the model prediction.

The Compact Linear Collider (CLIC) is a proposed successor to the LHC. The potential for charged and heavy neutral Higgs bosons at CLIC was investigated, in terms of both discovery and precision measurement of parameters like tanβ or the Higgs masses, up to and beyond 1 TeV, which would be challenging at the LHC

##### Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 61 p.
##### Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 702
##### Keyword
particle physics, Standard Model, beyond the Standard Model, supersymmetry, MSSM, Higgs physics, charged Higgs boson, LHC, ATLAS, ATLAS Semi-Conductor Tracker, SCT, tau lepton, Lorentz angle, CLIC
##### National Category
Subatomic Physics
##### Research subject
High Energy Physics
##### Identifiers
urn:nbn:se:uu:diva-111576 (URN)978-91-554-7693-9 (ISBN)
##### Public defence
2010-02-12, Polhemssalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
##### Supervisors
Available from: 2010-01-22 Created: 2009-12-17 Last updated: 2012-10-10
2. 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.
##### Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 696
##### Keyword
charged Higgs, tau, ATLAS, HEP, CERN, LHC, Particle Physics, Grid
##### National Category
Physical Sciences
##### Research subject
High Energy Physics
##### Identifiers
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)
##### Supervisors
Available from: 2009-12-22 Created: 2009-11-30 Last updated: 2009-12-22Bibliographically approved

#### Open Access in DiVA

No full text

http://cdsweb.cern.ch/record/1125884

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