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T: Fachverband Teilchenphysik

T 35: Top-Quarks 3

T 35.5: Talk

Monday, March 4, 2013, 17:45–18:00, HSZ-02

Studies of Systematic Uncertainties with Profile Likelihood Fits at ATLAS — Andrea Knue, Kevin Kröninger, Arnulf Quadt, and •Philipp Stolte — II. Physikalisches Institut, Georg-August-Universität Göttingen

Profile likelihood fits constitute a comparatively new and promising fitting technique which can be applied to a variety of measurements. Those fits are based on the idea of constraining relevant systematic effects via additional fit parameters, so-called nuisance parameters, using data. Each source of systematic uncertainties is associated with a nuisance parameter added to the statistical model. In contrast to a standard likelihood, a profile likelihood is then maximised with respect to these nuisance parameters.

In this talk, studies of systematic uncertainties with profile likelihood fits are presented in the context of a W boson polarisation measurement in top quark pair decays using data recorded with the ATLAS detector at the LHC.

The profile likelihood fits described in this talk are based on template fits, which are covered as a starting point. Emphasis is then placed on investigating the general performance and possible strengths of profile likelihood fits by testing various interpolation methods, but also on validating the stability and the modelling of the fit in more detail. It is furthermore briefly discussed which systematic effects can be associated with nuisance parameters.