February 24, 2021 Master Thesis Open Access

Ecker, Patrick

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    "description": "<p>One of the assumptions the standard model of particle physics makes is the lepton flavor universality.<br>\nThis assumes that the couplings of the gauge bosons do not depend on the flavor of the interacting lepton.<br>\nTaking 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 $.<br>\nThe combined result shows a $ 3.1\\sigma $ deviation from the value expected from the SM.<br>\nTo 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&nbsp; $ \\mathcal{R}(D^{(**)}) $ measurement is performed with the Belle dataset.<br>\n<br>\nTwo 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.<br>\nTo 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.<br>\nAdditionally, this thesis introduces a setup to measure the different $ B \\rightarrow D^{**} l \\nu $ branching fractions for each of the four different $D^{**} $ states.<br>\nBoth 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.</p>\n\n<p>&nbsp;</p>", 
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      "report_number": "ETP-KA/2021-03", 
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          "affiliation": "KIT/ETP", 
          "name": "Quast, G\u00fcnter"
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        {
          "affiliation": "Uni Bonn", 
          "name": "Bernlochner, Florian"
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    "title": "Study of $B \u2192 D^{**} l \\nu$ decays for a $R(D^{ (\u2217) })$ measurement at Belle"
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