Study of B meson decays into excited charmonium states at the LHCb experiment

In this research, two interconnected analysis are reported. The analysis are based on a data samples of proton-proton collisions, corresponding to an integrated luminosities of 1 and 2 fb$^{-1}$ , collected with the LHCb detector, at centre-of-mass energies of 7 and 8~TeV. In the first part the branching fractions of the $B^{0}\rightarrow\chi_{c1} K^{*0}$ and $B_{s}^{0}\rightarrow\chi_{c1}\phi$ decays are measured with respect to $B^{0}\rightarrow J/\psi K^{*0}$ и $B_{s}^{0}\rightarrow J/\psi\phi$ decays, and the ratio of branching fractions of $B^{0}\rightarrow\chi_{c2} K^{*0}$ and $B^{0}\rightarrow\chi_{c1} K^{*0}$ decays is measured. The decays were reconstructed using $\chi_{c1,2}\rightarrow J/\psi\gamma$, $J/\psi\to\mu^{+}\mu^{-}$, $K^{*0}\rightarrow K^{+}\pi^{-}$ and $\phi\rightarrow K^{+}K^{-}$ decay modes. The first observation of the $B_{s}^{0}\rightarrow\chi_{c1}\phi$ decay is performed. The measured ratios ${\cal B}(B^{0}\rightarrow\chi_{c1} K^{*0})/{\cal B}(B^{0}\rightarrow J/\psi K^{*0})$ and ${\cal B}(B^{0}\rightarrow\chi_{c2} K^{*0})/{\cal B}(B^{0}\rightarrow\chi_{c1} K^{*0})$ are compatible with, but more precise than, the results of the previous experiments. In the second part the ratio of branching fractions of the $X(3872)\rightarrow\psi(2S)\gamma$ and $X(3872)\rightarrow J/\psi\gamma$ decays was measured. The $X(3872)$ states were reconstructed in the $B^{+}\rightarrow X(3872)K^{+}$ decay using the $J/\psi\to\mu^{+}\mu^{-}$ and $\psi(2S)\to\mu^{+}\mu^{-}$ decay modes. The resulting ratio ${\cal B}(X(3872)\rightarrow\psi(2S)\gamma)/{\cal B}(X(3872)\rightarrow J/\psi\gamma)$ is compatible with, but more precise, than the previous measurements of the BaBar and Belle collaborations.