Thesis defense of Jan Langer

In this thesis, two measurements probing the Standard Model of particle physics in B->D*+D*- decays are presented. Both measurements are performed using proton-proton collision data recorded by the LHCb experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 9fb-1. The first analysis is a branching fraction measurement of the Bs->D*+D*- decay. The decay is observed with a significance of more than $10$ standard deviations. The absolute time-integrated Bs->D*+D*- branching fraction is measured to be B(Bs->D*+D*-) = (2.15 +- 0.26 +- 0.09 +- 0.06 +- 0.16) * 10^(-4) where the first uncertainty is statistical, the second systematic, the third the uncertainty of the fragmentation fraction ratio fs/fd and the fourth is due to the limited precision of the BdToDstDst branching fraction used in the normalisation.

The second analysis presented is the measurement of CP violation in BdToDstDst decays. As the final state is a mixture of CP-even and CP-odd states, the CP observable S(D*+D*-) is diluted. Therefore, an angular analysis is performed to determine the dilution factor. The current state of the analysis and its sensitivity are presented and discussed. With the current precision, the uncertainty of the measurement is expected to be statistically dominated.