Measurement of the branching ratio of Bs0 → K0S K0S decays with the LHCb experiment

Abstract

The presented thesis deals with the branching ratio measurement of the decay channel Bs0 → KS0 KS0 reconstructed as two charged pion pairs. The data correspond to an integrated luminosity of 5 fb^{-1} collected by the LHCb experiment in proton-proton collisions at the centre-of-mass energies of sqrt{s} = 7 TeV (1 fb^{-1}), 8 TeV (2 fb^{-1}) and 13 TeV (2 fb^{-1}). As normalisation channel the decay B0 → φKS0 is used in which the φ meson is reconstructed as two charged kaons. The branching ratio is determined to be BR(Bs0 → KS0 KS0) = [9.5 +- 1.9 (stat) +- 0.9 (syst) +- 0.9 (BR(B0 → φKS0) +- 0.5 (f_d/f_s)] * 10^{-6}, whereby the Bs0 → KS0 KS0 component has a significance of 7.24σ. The result is consistent with measurements of the BELLE collaboration within less than one standard deviation and compatible with Standard Model predictions. Furthermore, the analysis represents the first study of b hadrons decaying exclusively into long lived V^0 particles at the LHCb experiment.