Thesis defense of Gerwin Meier

High-precision measurements of observables of the Standard Model of particle physics, like the CKM matrix parameters, are key to answering the open questions of particle physics. The most precise CKM angle sin(2β) can be optimally determined by a decay-time dependent measurement of CP violation in B→ψKS0 decays. In this thesis data from B→J/ψ(→μμ)KS0, B→ψ(2S)(→μμ)KS0 and B→J/ψ(→ee)KS0 decays is analysed with KS0→π+π- collected at a centre-of-mass energy of √s = 13TeV with pp collisions by the LHCb experiment between 2015 and 2018. The data corresponds to an integrated luminosity of 6/fb and results in the combination of all three decays for the CP violation parameters in

S(ψKS0) = 0.717 +/- 0.013 (stat.) +/- 0.008 (syst.),
C(ψKS0) = 0.008 +/- 0.012 (stat.) +/- 0.003 (syst.),

where S corresponds to sin(2β). This is consistent with the Standard Model predictions and with previous measurements. Furthermore, this is the most precise single measurement and more precise than the current world average.

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