The decays $B^+\rightarrow J/\psi \pi^+ \pi^- K^+$ are studied using a data set corresponding to an integrated luminosity of 9fb$^{ -1}$ collected with the LHCb detector in proton-proton collisions between 2011 and 2018. 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 $B^+\rightarrow \psi_2(3823)K^+$ with $\psi_2(3823)\rightarrow J\psi\pi^+\pi^-$ is observed for the first time with a significance of 5.1 standard deviations. The mass differences between the $\psi_2(3823)$, $\chi_{ c1}(3872)$ and $\psi(2S)$ states are measured to be $$ \begin{ array}{ rcl} m_{ \chi_{ c1(3872)}} - m_{ \psi_2(3823)} &= & 47.50 \pm 0.53 \pm 0.13\,\mathrm{ MeV/}c^2\,, \\ m_{ \psi_2(3823)} - m_{ \psi(2S)} &= & 137.98 \pm 0.53 \pm 0.14\,\mathrm{ MeV/}c^2\,, \\ m_{ \chi_{ c1}(3872)} - m_{ \psi(2S)} &= & 185.49 \pm 0.06 \pm 0.03\,\mathrm{ MeV/}c^2\,, \end{ array} $$ resulting in the most precise determination of the $\chi_{ c1}(3782)$ mass. The width of the $\psi_2(3823)$ state is found to be below 5.2MeV at 90\% confidence level. The Breit-Wigner width of the $\chi_{ c1}(3872)$ state is measured to be $$ \Gamma^{ \mathrm{ BW}}_{ \chi_{ c1}(3872)} = 0.96^{ +0.19}_{ -0.18}\pm0.21 \mathrm{ MeV},$$ which is inconsistent with zero by 5.5 standard deviations.
Categories: hep-ex