Studies of the $B^{0}_{s}-\overline{B}^{0}_{s}$ in the CMS experiment at the LHC

The B0s-B0sbar system was investigated using the J/ψ(μ+μ−)φ(K+K−) decay channel. Using 2010 CMS data, corresponding to an integrated luminosity of 40 1/pb, the B0s invariant mass peak was reconstructed and the B0s differential cross section as a function of its transverse momentum and rapidity were measured. Using 2011 CMS data, corresponding to an integrated luminosity of 5 1/fb, the difference of the decay widths between the two B0s mass eigenstates ∆Γs was measured. With the 2012 CMS data, corresponding to an integrated luminosity of 20 1/fb, the CP-violating weak phase φs and the decay width difference ∆Γs of B0s were measured. The most important result of this thesis is the measurement of the CP-violating phase φs, which was found to be φs = −0.075 ± 0.097 (stat.) ± 0.031 (syst.).