Thesis defense of Kevin Heinicke

In this thesis, a measurement of the Bs-Bsbar oscillation frequency, DeltaMs, is presented. The oscillation frequency provides constraints on the parameters of the CKM matrix and is a crucial input for decay-time dependent measurements of CP violation with Bs mesons. The study is performed with a data sample of 378 700 decays of Bs → DsPi, which is extracted from a sample of proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6/fb. The data sample was recorded between 2015 and 2018 using the LHCb experiment. An unbinned, weighted maximum-likelihood fit is used to determine the frequency as DeltaMs = (17.7683 ± 0.0051 ± 0.0032)/ps. The result is one of the most precise measurements of the LHCb experiment to date. It is in agreement with current Standard Model predictions.