Observation of the decay $\overline{B_s^0} \rightarrow \chi_{c2} K^+ K^- $ in the $\varphi$ mass region

TL;DR

This paper reports the first observation of the decay ar{B}_s^0 2 K^+ K^- in the  region and measures its branching fraction relative to ar{B}_s^0 1 K^+ K^-, also providing a precise measurement of the B_s^0 mass.

Contribution

The study provides the first observation of the ar{B}_s^0 2 K^+ K^- decay mode and measures its branching ratio relative to the ar{B}_s^0 1 K^+ K^- decay, along with an improved B_s^0 mass measurement.

Findings

Branching fraction ratio: (17.1 0 3.1 0 0.4 0 0.9)%

B_s^0 mass: 5366.83 0 0.25 0 0.27 MeV/c^2

Observation of the ar{B}_s^0 2 K^+ K^- decay mode.

Abstract

The $\overline{B_s^0} \rightarrow \chi_{c2} K^+ K^- $ decay mode is observed and its branching fraction relative to the corresponding $\chi_{c1}$ decay mode, in a $\pm 15 \textrm{MeV}/c^2$ window around the $\phi$ mass, is found to be $\frac{\mathcal{B}(\overline{B_s^0} \rightarrow \chi_{c2} K^+ K^-) }{ \mathcal{B}(\overline{B_s^0} \rightarrow \chi_{c1} K^+ K^-)} = (17.1 \pm 3.1 \pm 0.4 \pm 0.9)\%,$ where the first uncertainty is statistical, the second systematic and the third due to the knowledge of the branching fractions of radiative $\chi_c$ decays. The decay mode $\overline{B_s^0} \rightarrow \chi_{c1} K^+ K^- $ allows the $ B_s^0$ mass to be measured as $m(B_s^0) = 5366.83 \pm 0.25 \pm 0.27 \, \textrm{MeV}/c^2,$ where the first uncertainty is statistical and the second systematic. A combination of this result with other LHCb determinations of the $B_s^0$ mass is made.