Поиск новых распадов прелестных частиц в эксперименте LHCb

The searches for $\Lambda_b^0~\to~\chi_{c1}(3872)pK^-$ and $B^+\to\psi_2(3823)K^+$ decays are presented in this thesis. Using proton-proton collision data, collected with the LHCb detector and corresponding to 4.9 fb$^{-1}$ of integrated luminosity, the decay $\Lambda_b^0~\to~\chi_{c1}(3872)pK^-$ with $\chi_{c1}(3872)~\to~J/\psi\pi^+\pi^-$ is observed for the first time with a significance of 7.2 standard deviations. The branching fraction of this decay with respect to that of the $\Lambda_b^0\to\psi(2S)pK^-$ decay mode, where the $\psi(2S)$ meson is reconstructed in the $J/\psi\pi^+\pi^-$ final state, is measured. The largest contributions to the $\Lambda^0_b\to J/\psi\pi^+\pi^-pK^-$ decay is found to be from the two-body $\chi_{c1}(3872)\Lambda(1520)$ intermediate state. The decays $B^+\to J/\psi\pi^+\pi^-K^+$ are studied using a data set corresponding to an integrated luminosity of $9$fb$^{-1}$. Precise measurements of the ratios of branching fractions with the intermediate $\psi_2(3823)$, $\chi_{c1}(3872)$ and $\psi(2S)$ states are reported. The decay of $B^+\to\psi_2(3823)K^+$ with $\psi_2(3823)~\to~J/\psi\pi^+\pi^-$ is observed for the first time with a significance of 5.1 standard deviations. The large statistics provided the possibility for determination of the resonance parameters for the $\chi_{c1}(3872)$ state with an unprecedented precision. Using a Breit-Wigner parametrization the mass differences between the $\psi_2(3823)$, $\chi_{c1}(3872)$ and $\psi(2S)$ states are measured, resulting in the most precise determination of the $\chi_{c1}(3872)$ and $\psi_2(3823)$ masses. The Breit-Wigner width of the $\chi_{c1}(3872)$ state is determined for the first time, which is inconsistent with zero by 5.5 standard deviations. The width of the $\psi_2(3823)$ state is found to be consistent with zero and an upper limit is set.