Study of $B^0_s \rightarrow J/\psi\pi^+\pi^-K^+K^-$ decays

TL;DR

This paper reports the first observation of specific decay modes of the $B^0_s$ meson, measures their branching ratios, discovers a new structure called $X(4740)$ in the $J/ auphi$ spectrum, and provides the most precise mass measurement of the $B^0_s$ meson.

Contribution

It presents the first observation of $B^0_s ightarrow J/ au extpi^+ extpi^-K^+K^-$ decay modes and characterizes a new resonance $X(4740)$, with precise measurements of branching ratios and meson mass.

Findings

First observation of $B^0_s ightarrow J/ au K^{ extast0} ar{K}^{ extast0}$ and $B^0_s ightarrow ext{ extc{c}1}(3872)K^+K^-$ decays.

Discovery of a new structure $X(4740)$ in the $J/ auphi$ spectrum.

Most precise measurement of the $B^0_s$ meson mass.

Abstract

The decays $B^0_s \rightarrow J/\psi \pi^+\pi^- K^+ K^-$ are studied using a data set corresponding to an integrated luminosity of 9fb$^{-1}$, collected with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13TeV. The decays $B^0_s \rightarrow J/\psi K^{\ast0} \bar{K}^{\ast0}$ and $B^0_s \rightarrow \chi_{c1}(3872)K^+K^-$, where the $K^+K^-$ pair does not originate from a $\phi$ meson, are observed for the first time. Precise measurements of the ratios of branching fractions between intermediate $\chi_{c1}(3872)\phi$, $J/\psi K^{\ast0}\bar{K}^{\ast0}$, $\psi(2S)\phi$ and $\chi_{c1}(3872)K^+K^-$ states are reported. A structure, denoted as $X(4740)$, is observed in the $J/\psi\phi$ mass spectrum and, assuming a Breit-Wigner parameterisation, its mass and width are determined to be \begin{eqnarray*} m_{X(4740)} & = & 4741 \pm 6 \pm 6\,{\mathrm{MeV}}/c^2 \,, \\ \Gamma_{X(4740)} & = & 53 \pm 15 \pm 11\,{\mathrm{MeV}} \,, \end{eqnarray*} where the first uncertainty is statistical and the second is systematic. In addition, the most precise single measurement of the mass of the $B^0_s$ meson is performed and gives a value of $$ m_{B^0_s} = 5366.98 \pm 0.07 \pm 0.13\,{\mathrm{MeV}}/c^2\,. $$