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Humboldt-Universität zu Berlin - Mathematisch-Naturwissen­schaft­liche Fakultät - Experimentelle Elementarteilchenphysik

Humboldt-Universität zu Berlin | Mathematisch-Naturwissen­schaft­liche Fakultät | Institut für Physik | Experimentelle Elementarteilchenphysik | ATLAS | Theses | From Top to Bottom: Calibration of b-Tagging Algorithms via a Kinematic Fit of Top Quark Pair Decays

Lukas Heinrich (2012)

From Top to Bottom: Calibration of b-Tagging Algorithms via a Kinematic Fit of Top Quark Pair Decays

Master thesis, Humboldt-Universität zu Berlin.

For Standard Model physics and searches for physics beyond the Standard Model,
physicists rely on the analysis of the final states of the proton-proton scatterings
produced at the LHC. Many of the interesting final states such as Higgs boson and

top quark decays or the decay cascades that Supersymmetry, a popular extension

of the Standard Model, predicts feature the presence of heavy quarks such as the

bottom quark. Therefore a powerful and efficient identification of the presence of

these quarks, referred to as b-tagging, greatly facilitates these analyses. In order

to observe new physics, e.g. as excesses over known backgrounds, one must have

a very good understanding of the Standard Model prediction. While the use of

algorithmic identification techniques for heavy quarks, referred to as b-tagging, can

reduce backgrounds to a large degree, it oftentimes is also a major source of system-

atic uncertainty for the number of events predicted to be observed by simulation,

as the performance of these techniques in actual collision events can deviate from

that in the simulation programs. Therefore these identification techniques must be

calibrated using data samples that closely mimic the environment where they are

used in the analyses. The calibration of b-tagging algorithms using a sample of top

quark pair decays via a method that aims to reduce the systematic uncertainties by

exploiting our knowledge of the kinematics of such decays is presented here.