Search for electroweak single top-quark production with the CDF II experiment Page: 4 of 204
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ii
corresponding to an integrated luminosity of ~ 1 fb-1, a sensitivity between 2a and
3a is expected.
At the Tevatron, two processes contribute significantly to the production of sin-
gle top-quarks: (1) production via t-channel, also called W-gluon fusion, and (2)
production via s-channel, known as well as W* process. To distinguish the two
single top-quark production channels from the various backgrounds, we use neural
networks to combine many quantities into one discriminating variable. The out-
put distributions of simulated events are used to create templates which are fitted
to the output distribution of observed events to determine the cross section. We
pursue two different approaches: The first is a combined search of the production
modes via t- and s-channel with the assumption that the ratio of the cross sections
is as predicted by the standard model. The second is a separate search in which
the cross sections of t- and s-channel production are determined separately and
simultaneously.
One important improvement to previous searches for single top-quark production,
which was developed in the context of this thesis, is the extension of the standard
method of b-quark jet identification. The identification of b-quark jets is crucial
for top-quark physics, since the top quark decays with a branching fraction of al-
most 100% into a W boson and a b quark. The standard identification method of
reconstructing a secondary vertex mainly utilizes the long lifetime of b hadrons. To
further reject secondary vertices due to decaying c hadrons or false reconstruction,
the identification of b jets is extended by exploiting many characteristics of b hadrons
using a neural network.
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Richter, Svenja. Search for electroweak single top-quark production with the CDF II experiment, thesis or dissertation, November 1, 2007; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc901832/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.