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T: Fachverband Teilchenphysik

T 34: Top-Quark: Produktion 3

T 34.5: Talk

Wednesday, February 29, 2012, 17:45–18:00, ZHG 104

Treatment of Systematic Uncertainties with the Help of a Profile Likelihood Fit — Kevin Kröninger¹, Arnulf Quadt¹, and •Philipp Stolte^1,2 — ¹Georg-August-Universität Göttingen — ²NIKHEF, Amsterdam, Niederlande

One of the most important measurements performed in the field of particle physics is the measurement of a signal cross-section - a very challenging task since various systematic uncertainties need to be taken into account. For instance, different energy scales or the background normalisation have to be considered.

In order to facilitate the effort of such a cross-section measurement, a profile likelihood fit instead of a standard likelihood fit can be used. The most striking characteristic of a profile likelihood fit is that the different systematic variations enter in the minimisation process of the likelihood itself as additional fit parameters. These so-called nuisance parameters adjust the size of the corresponding systematics since the resulting fit values constitute that quantity which best fits the data. Thus, a profile likelihood fit serves to constrain the various systematic uncertainties directly with the help of the given data.

In this talk, a profile likelihood fit serving to measure the cross-section of single top quarks in the Wt production channel using data recorded with the ATLAS detector at the LHC is presented. In the studies performed so far, it was put emphasis on the semileptonic decay channel with a muon in the final state.