Experimental Flavor Physics

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Bachelor Thesis Topics


Optimization of inclusive B meson reconstruction (topic not available any more)

At the B factory experiment Belle II B mesons are produced in the reaction e+ e- -> Y(4S) -> B anti-B. The fact that nothing else than two B mesons are produced is exploited in many analyses. These analyses require the reconstruction of one of the B mesons to infer properties of the decay of the other B meson. A reconstruction approach with high efficiency is an inclusive method where all momenta of particles remaining after the reconstruction of the other B meson are summed up. The selection and identification criteria of particles affect the quality of the reconstruction and should be optimized, potentially using machine learning techniques. The inclusive reconstruction method can be used, for exmple, to measure B -> D(*) tau nu decays where hints for new physics have been observed.

Development of an inclusive reconstruction of final states with strangeness

Some interesting tensions with respect to the standard model prediction 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. Methods for an inclusive Xs reconstruction, potentially using machine learning techniques, should be developed.

Sensitivity to the decay K0S -> l+ l- at Belle II (topic not available any more)

The decay of a K0S to a pair of leptons is highly suppressed in the standard model, but could be enhanced in case of new physics contributions to the s -> d l+ l- transition. So far only limits on the branching ratio could be set. The sensitivity to the decay K0S -> l+ l- at Belle II should be studied.

Reconstruction of D mesons in first Belle II data (topic not available any more)

The B mesons produced in e+ e- -> Y(4S) -> B anti-B reactions at the SuperKEKB accelerator are reconstructed from the decay products detected in the Belle II detector. The B mesons dominantly decay to ground state or excited D mesons. Using data of the first Belle II physics run, D mesons should be reconstructed and their properties compared to simulation. Excited D mesons play an important role in the measurement of B -> D(*) tau nu decays where hints for new physics have been observed.

Optimization of track reconstruction (topic not available any more)

The trajectories of charged particles close to the interaction point are reconstructed from hits in a silicon strip detector. The hits in different layers first have to be assigned to track candidates which is a combinatorial problem. To keep the computational effort at a reasonable level, relations between detector parts that may be hit by the same track are calculated. The robustness and optimizations of this predefined map should be studied.

Monte-Carlo matching for inclusive decays

In several analyses only some of the final state particles of the decays of interest are directly detected. The remaining final state particles are inferred by inclusive reconstruction techniques. To verify that such an inclusive reconstruction is correct, a matching to simulated particles is done in Monte-Carlo data. An algorithm for such a matching should be developed. It requires C++ programming skills.

Optimization of background simulation with machine learning techniques (topic not available any more)

Rare processes are a promising way to search for physics beyond the standard model. A challenge in the analysis of such processes 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. The applicability of techniques developed for the Belle II experiment at ATLAS should be studied.


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