Experimental Flavor Physics

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Master Thesis Topics

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Search for B -> l nu at Belle (topic not available any more)

The Belle experiment has the world's largest Y(4S) dataset. Because of recent advances in the Belle II software it is now possible to analyze this dataset with the new framework. A search for the rare decays B -> l nu, where l is a muon or electron, may be the first analysis to exploit this opportunity and would thus be a milestone for the Belle and Belle II experiments. An observation of the decay with the Belle dataset would be a clear sign of new physics.

Test of isospin symmetry at Belle (topic not available any 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 rates to B+ B- and B0 anti-B0 pairs. These branching fractions are an essential input for many other results.

Improved measurement of CP violation with a combination of tagging and vertex fit

The measurement of time-dependent CP asymmetries in B0 meson decays is one of the main tasks of B-factory experiments. Essential components for such measurements are the determination of the decay vertex and the flavor of the second B meson in the event. So far both tasks have been addressed by independent algorithms, but information whether a particle comes directly from the B decay or from a B daughter particle decay is relevant for both. A new algorithm which combines the determination of both quantities of interest may provide a significant improvement of CP violation measurements. A measurement of CP violation in the golden mode B0 -> J/psi KS will serve as bencchmark.

Search for B -> K(*) nu nu with inclusive tag B reconstruction

The fact that only two B mesons are produced in e+e- -> Y(4S) events makes the future Belle II experiment a unique device to measure several B mesons decays involving undetected neutrinos. One of them is the rare decay B -> K(*) nu nu which is sensitive to physics beyond the standard model.  The trick for these measurements is to reconstruct all decay particles of one of the B mesons. A new algorithm for the full reconstruction of a B meson was developed for Belle II and comprises over 1000 decay modes. However, inclusive B meson reconstruction techniques where the full B meson decay chain is not explicitly reconstructed have shown similar performance in Belle measurement. Thus a considerable gain in sensitivity can be expected by developing an inclusive B reconstruction algorithm for Belle II and integrating it in the existing framework for the exclusive reconstruction.

Real-time grid production quality monitoring

Because of the large amount of data from particle physics experiments their analysis requires to run thousands of jobs on computing resources distributed around the world. Often the quality of the produced output data is only checked when (a large fraction of) the jobs are finished. If then a problem is detected that requires a resubmission of the jobs it means that huge resources have been wasted in the first iteration. To provide a faster feedback on the data quality a system should be developed for the Belle II experiment which provides quality indicators, like monitoring histograms or error rates, while the jobs are still running. This requires well coordinated interplay between the software framework and the distributed computing system.

Integration of user software in grid production system

The software to analyze particle physics data is usually written by an individual or small group specifically for each analysis. This development is often done on a local desktop or laptop and tested only on a small dataset, if at all, before it is applied to large datasets via the submission of grid jobs. Before the user analysis software can be used to process the world-wide distributed data it has to be made available on the relevant grid sites. Moreover it may be beneficial to perform some quality and benchmark tests before starting a large production. Users and resource providers would profit from such an integration of the user analysis software in the grid production system.