CERN Accelerating science

Thesis
Report number	CERN-THESIS-2010-330
Title	Search for a signal of quarks of a fourth generation in same-sign dilepton final states with ATLAS
Author(s)	Wendland, Dennis (Humboldt U., Berlin)
Publication	2010 - 153.
Thesis note	Master : Humboldt U., Berlin : 2010
Thesis supervisor(s)	Lacker, Heiko
Note	presented 5 October 2010
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Abstract	Currently, a fourth generation of fermions can not be excluded, neither based on theoretical arguments nor by experimental constraints. In this thesis a method developed to extract a signal coming from quarks of such a fourth family with the ATLAS detector at the Large Hadron Collider is presented. The search is performed with the selection of final states containing two same-sign charged leptons, which is a rare Standard Model signature. The signal extraction method presented is a cut-based counting analysis and includes a data-driven background estimation. The analysis is tested on pseudo data which were created from simulated data sets. Furthermore, the uncertainties on the obtained results are estimated by a so-called "Toy Monte Carlo Study". An optimisation of the cuts is finally performed using a multivariate analysis in order to maximise the significance.

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