Observation of B$^0$ $\rightarrow $ $\uppsi $(2s)k$^0_\mathrm {s}\uppi ^+\uppi ^-$ and B$^0_\mathrm {s}$ $\rightarrow $ $\uppsi $(2s)k$^0_\mathrm {S}$ Decays

AbstractUsing a data sample of $\sqrt{s}=13\,\text {TeV}$ s = 13 TeV proton-proton collisions collected by the CMS experiment at the LHC in 2017 and 2018 with an integrated luminosity of $103\text {~fb}^{-1}$ 103 fb - 1 , the $\text {B}^{0}_{\mathrm{s}} \rightarrow \uppsi (\text {2S})\text {K}_\mathrm{S}^{0}$ B s 0 → ψ ( 2S ) K S 0 and $\text {B}^{0} \rightarrow \uppsi (\text {2S})\text {K}_\mathrm{S}^{0} \uppi ^+\uppi ^-$ B 0 → ψ ( 2S ) K S 0 π + π - decays are observed with significances exceeding 5 standard deviations. The resulting branching fraction ratios, measured for the first time, correspond to ${\mathcal {B}}(\text {B}^{0}_{\mathrm{s}} \rightarrow \uppsi (\text {2S})K_\mathrm{S}^{0})/{\mathcal {B}}(\text {B}^{0}\rightarrow \uppsi (\text {2S})K_\mathrm{S}^{0}) = (3.33 \pm 0.69 (\text {stat})\, \pm 0.11\,(\text {syst}) \pm 0.34\,(f_{\mathrm{s}}/f_{\mathrm{d}})) \times 10^{-2}$ B ( B s 0 → ψ ( 2S ) K S 0 ) / B ( B 0 → ψ ( 2S ) K S 0 ) = ( 3.33 ± 0.69 ( stat ) ± 0.11 ( syst ) ± 0.34 ( f s / f d ) ) × 10 - 2 and ${\mathcal {B}}(\text {B}^{0} \rightarrow \uppsi (\text {2S})\text {K}_\mathrm{S}^{0} \uppi ^{+} \uppi ^{-})/ {\mathcal {B}}(\text {B}^{0} \rightarrow \uppsi (\text {2S})\text {K}^{0}_{\mathrm{S}}) = 0.480 \pm 0.013\,(\text {stat}) \pm 0.032\,(\text {syst})$ B ( B 0 → ψ ( 2S ) K S 0 π + π - ) / B ( B 0 → ψ ( 2S ) K S 0 ) = 0.480 ± 0.013 ( stat ) ± 0.032 ( syst ) , where the last uncertainty in the first ratio is related to the uncertainty in the ratio of production cross sections of $\hbox {B}^{0}_{\mathrm{s}}$ B s 0 and $\hbox {B}^{0}$ B 0 mesons, $f_{\mathrm{s}}/f_{\mathrm{d}}$ f s / f d .