Observation of B 0 → ψ (2S)K S 0 π + π - and B s 0 → ψ (2S)K S 0 decays

Abstract

Using a data sample of $\sqrt{s}=13\text{TeV}$ proton-proton collisions collected by the CMS experiment at the LHC in 2017 and 2018 with an integrated luminosity of $103{\text{fb}}^{-1}$ , the ${\text{B}}_s^0\to \psi \left(\text{2S}\right){\text{K}}_S^0$ and ${\text{B}}^0\to \psi \left(\text{2S}\right){\text{K}}_S^0{\pi }^{+}{\pi }^{-}$ decays are observed with significances exceeding 5 standard deviations. The resulting branching fraction ratios, measured for the first time, correspond to $B({\text{B}}_s^0\to \psi \left(\text{2S}\right)K_S^0)/B({\text{B}}^0\to \psi \left(\text{2S}\right)K_S^0)=(3.33\pm 0.69\left(\text{stat}\right)\pm 0.11\left(\text{syst}\right)\pm 0.34(f_s/f_d))\times {10}^{-2}$ and $B({\text{B}}^0\to \psi \left(\text{2S}\right){\text{K}}_S^0{\pi }^{+}{\pi }^{-})/B({\text{B}}^0\to \psi \left(\text{2S}\right){\text{K}}_S^0)=0.480\pm 0.013\left(\text{stat}\right)\pm 0.032\left(\text{syst}\right)$ , where the last uncertainty in the first ratio is related to the uncertainty in the ratio of production cross sections of ${\text{B}}_s^0$ and ${\text{B}}^0$ mesons, $f_s/f_d$ .