February 24, 2021 Master Thesis Open Access

Ecker, Patrick

MARC21 XML Export

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    <subfield code="a">&lt;p&gt;One of the assumptions the standard model of particle physics makes is the lepton flavor universality.&lt;br&gt;
This assumes that the couplings of the gauge bosons do not depend on the flavor of the interacting lepton.&lt;br&gt;
Taking this assumption into account, one can calculate the branching fraction ratios of the semileptonic $ B \rightarrow D^{(**)} \tau \nu $ decay to the $ B \rightarrow D^{(**)} l \nu $ decay, with $ l $ being one of the light leptons $ e $ or $ \mu $.&lt;br&gt;
The combined result shows a $ 3.1\sigma $ deviation from the value expected from the SM.&lt;br&gt;
To check whether the discrepancy reported by the previous $ \mathcal{R}(D^{(**)}) $ measurements is actually there or caused by a systematic error in the measurement, a new&amp;nbsp; $ \mathcal{R}(D^{(**)}) $ measurement is performed with the Belle dataset.&lt;br&gt;
&lt;br&gt;
Two of the main systematic uncertainties, which are reported for the previous measurements, are the limited knowledge about both the shapes and the branching fractions of the $ B \rightarrow D^{**} l \nu $ decays.&lt;br&gt;
To reduce the above mentioned uncertainties for the $ \mathcal{R}(D^{(**)}) $ analysis, this thesis provides studies on the form factor modeling of the four different $ D^{**} $ states.&lt;br&gt;
Additionally, this thesis introduces a setup to measure the different $ B \rightarrow D^{**} l \nu $ branching fractions for each of the four different $D^{**} $ states.&lt;br&gt;
Both the form factor study and the branching fraction measurement are expected to improve the understanding of the decay $ B \rightarrow D^{**} l \nu $ and consequently reduce the systematic uncertainty on the underlying $ \mathcal{R}(D^{(**)}) $ measurement.&lt;/p&gt;

&lt;p&gt;&amp;nbsp;&lt;/p&gt;</subfield>
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