Abstract

Although the Standard Model of Particle Physics is one of the most successful theories, it still leaves some open questions, e.g. it doesn’t include gravity and is only able to describe about 4.9% of the energy in our universe. Therefore, many experiments are searching for physics beyond the Standard Model. One possibility to investigate deviations from its predictions is the study of the violation of the CP-symmetry (turning a particle into its anti-particle and mirroring its position in space) in calculating the CP violating phase. This can be achieved using the Branching fraction (which is the ratio for a particle decaying into its decay-products) of the decay of the Bs-meson into a J/Psi-meson and a Phi-meson.

The Belle experiment is located at the asymmetric particle collider KEKb in Tsubaka (Japan). This accelerator is the world’s largest electron-positron collider especially designed for creating B-anti-B-meson pairs or the heavier Bs-anti-Bs-meson pairs. It has collected a world-wide unique data sample of B-meson and Bs-meson decays at electron-positron-colliders.

The aim of this work was the calculation of the Branching fraction for the decay of the Bs-meson into a J/Psi-meson and a Phi-meson with the subdecay of the J/Psi-meson into an electron-positron or muon-anti-muon pair and the subdecay of the Phi-meson into a kaon-anti-kaon pair.

The reconstruction method and signal yield extraction was developed on simulated Monte Carlo data before it was used on real data. The signal yield extraction was performed with a 2D likelihood fit in the DeltaE- (energy-deviation of the Bs-meson to the collision-energy) and the Phi-mass-distribution. The influences of the non-resonant decay of the Bs-meson into a J/psi-meson and a kaon-anti-kaon pair were mostly sorted out during the reconstruction and the two different subdecays of the J/Psi-meson were treated separately throughout the whole analysis.

This result of the calculated Branching ratio is within the error range of previous analysis of the Particle Data Group PDG, the LHCb Collaboration at CERN (Geneva), the CDF Collaboration at Fermilab (Chicago) and the Belle Collaboration (Tsubaka).