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First determination of the electric charge of the top quark

Per Hansson
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Abstract

In this thesis, the first determination of the electric charge of the top quark is presented using 370pb-1 of data recorded by the D0 detector at the Fermilab Tevatron accelerator. ttbar events are selected with one isolated electron or muon and at least four jets out of which two are b-tagged by reconstruction of a secondary decay vertex (SVT). The method is based on the discrimination between b- and bbar-quark jets using a jet charge algorithm applied to SVT-tagged jets. A method to calibrate the jet charge algorithm with data is developed. A constrained kinematic fit is performed to associate the W bosons to the correct b-quark jets in the event and extract the top quark electric charge. The data is in good agreement with the Standard Model top quark electric charge of 2e/3. The scenario where the selected sample is solely composed of an exotic quark Q with charge 4e/3 is excluded at 92% confidence level. Using a Bayesian approach, an upper limit on the fraction of exotic quarks rho < 0.80 at 90% confidence level is obtained.

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Per Hansson. 2007-02-01. First determination of the electric charge of the top quark. https://arxiv.org/abs/hep-ex/0702004

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