Experimental Flavor Physics

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Bachelor Thesis Topics

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Sensitivity studies for the test of isospin symmetry in Y(4S) -> B+ B- decays at Belle (topic not available and more)

For the reaction e+ e- -> Y(4S) -> B anti-B it is often assumed that pairs of charged and neutral B mesons are produced at equal rate as expected in case of isospin symmetry. But isopsin is only an approximate symmetry. With the world's largest Y(4S) dataset of the Belle experiment it will be possible to make an improved measurement of the decay rate to B+ B- pairs. The same experimental technique cannot be applied directly for decays to B0 anti-B0 pairs and options to improve the precision of the measurement should be investigated. The branching fraction is an essential input for many other results and the precision that could be reached should be estimated.

Optimization of background identification with machine learning techniques (topic not available and more)

The decay B -> K(*) nu anti-nu is sensitive to contributions from physics beyond the standard model, but only the Belle II experiment will be able to observe this decay. A challenge in the analysis of this decay is the understanding of backgrounds which requires huge samples of simulated events. To efficiently obtain these samples, background events are selected before the computationally expensive detector response is simulated. Various input variabales for multivariate techniques for an optimization of the selection should be studied.

Sensitivity studies for B -> Xs l+ l- measurements at Belle II (topic not available and more)

Some interesting discrepancies with respect to the standrd model prediction at the level of 2 standard deviations are observed in B -> K(*) l+ l- decays. A further step to make progress in this area would be a measurement of the inclusive decay where all final states with a strange quark (Xs) are reconstructed instead of a kaon. The experimental techniques and sensitivities of such a measurement at Belle II should be studied.

Feasability of photon polarization measurement (topic not available and more)

The decay B -> K* gamma is sensitive to contributions from physics beyond the standard model. In particular the polarization of the photon is of interest. It should be investigated whether a measurement of the photon polarization is feasible at Belle II.

Sensitivity studies for a B -> l ν γ  measurement at Belle II

The decay B -> l ν γ is sensitive to the internal structure o the B meson. The parameter λB that can be calculated from the branching fraction of this decay is an important parameter for theoretical calculations. So far the decay was not observed. The sensitivity that can be reached at Belle II should be studied.

Vertex fitting algorithms survey

A precise knowledge of the origin of particles is important for many particle physics measurements. Several tools have been developed for determining which particles come from which vertex and for getting the best parameters for the vertex positions and the momenta of the decay particles. Most of the vertex fitter tools, which vary in functionality, interface, and execution speed, were developed for specific experiments. These tools should be systematically evaluated and optimized if needed.

Averaging of measurements

The same physical quantities are often measured by different experiments or with different methods. To optimally exploit the measurements they are combined. In the averaging procedure has to take into account the correlations between the measurements. A survey of existing methods should be done and the results applied to the tools of the heavy Flavor Averaging Group for B to charm decays.


A structured program is offered for the bachelor theses in the summer semester.