Measurement of the polarisation amplitudes in B0 → J/ψK*(892)0 decays with the LHCb experiment

In this thesis a measurement of the polarisation amplitudes and the corresponding strong phases of the decay B0→J/ψ(μ+μ-)K*(892)0(K+π-) is presented. Studying B0→J/ψ(μ+μ-)K*(892)0(K+π-) and anti B0→J/ψ(μ+μ-) anti K*(892)0(K-π+) decays separately allows for the measurement of direct CP violation. The Standard Model of particle physics does not predict any CP-violating processes for this decay channel. Thus, this analysis also serves as a search for new phenomena beyond the Standard Model. The measurement is performed using the full data sample collected with the LHCb detector in 2011 taken in proton-proton collisions at a centre-of-mass energy of 7 TeV corresponding to an integrated luminosity of approximately 1.0 fb-1. The determination of the polarisation amplitudes requires an angular analysis of the final state particles to disentangle the three possible angular momentum states. The observables are obtained using a four-dimensional maximum likelihood fit depending on the three decay angles and the decay time of the B0 meson. The values of the polarisation amplitudes and corresponding phases are determined to be R parallel = 0.227 ± 0.004 ± 0.011, R perpendicularto = 0.201 ± 0.004 ± 0.008, δ parallel = -2.94 ± 0.02 ± 0.03 and δ perpendicularto = 2.94 ± 0.02 ± 0.02, where the errors are statistical and systematic, respectively. The fit is performed in four bins of the K+π- invariant mass to measure the fraction of the non-resonant K+π-, so-called S-wave, contribution. Averaged over all mass bins, it is measured to be FS=(6.4±0.3±1.0)%. By determining the phase difference between the resonant P-wave and the S-wave contributions in the four mass bins a two-fold ambiguity in the strong phases is resolved. Furthermore, no evidence for CP violation is observed.