Measurement of the decays $B_s^0\to J/\psi \varphi (1020)$, $B_s^0\to J/\psi f_2^{\prime }(1525)$ and $B_s^0\to J/\psi K^{+}{K}^{-}$ at Belle

We report a measurement of the branching fraction of the decay $B_s^0\to J/\psi \varphi (1020)$, evidence and a branching fraction measurement for $B_s^0\to J/\psi f_2^{\prime }(1525)$, and the determination of the total $B_s^0\to J/\psi K^{+}{K}^{-}$ branching fraction, including the resonant and nonresonant contributions to the $K^{+}{K}^{-}$ channel. We also determine the $S$-wave contribution within the $\varphi (1020)$ mass region. The absolute branching fractions are $\mathcal{B}[B_s^0\to J/\psi \varphi (1020)]=(1.25\pm 0.07(\mathrm{stat})\pm 0.08(\mathrm{syst})\pm 0.22(f_s))\times {10}^{-3}$, $\mathcal{B}[B_s^0\to J/\psi f_2^{\prime }(1525)]=(0.26\pm 0.06(\mathrm{stat})\pm 0.02(\mathrm{syst})\pm 0.05(f_s))\times {10}^{-3}$, and $\mathcal{B}[B_s^0\to J/\psi K^{+}{K}^{-}]=(1.01\pm 0.09(\mathrm{stat})\pm 0.10(\mathrm{syst})\pm 0.18(f_s))\times {10}^{-3}$, where the last systematic error is due to the branching fraction of $b\overline{b}\to B_s^{(*)}{B}_s^{(*)}$. The branching fraction ratio is found to be $\mathcal{B}[B_s^0\to J/\psi f_2^{\prime }(1525)]/\mathcal{B}[B_s^0\to J/\psi \varphi (1020)]=(21.5\pm 4.9(\mathrm{stat})\pm 2.6(\mathrm{syst}))\%$. All results are based on a $121.4{\mathrm{fb}}^{-1}$ data sample collected at the ${\rm Y}(5S)$ resonance by the Belle experiment at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

Figure 1

Projection of the fit in $\Delta E$ for (a) $J/\psi \to e^{+}{e}^{-}$ and (b) $J/\psi \to {\mu }^{+}{\mu }^{-}$ events. The black points with error bars are the data and the upper solid line corresponds to the entire PDF model. From top to bottom, the peaking components are $J/\psi \varphi (1020)$, $J/\psi (K^{+}{K}^{-}{)}_{\mathrm{other}}$, and $J/\psi f_2^{\prime }(1525)$. Background is shown by the lower solid line.

Figure 2

Projection of the fit in $M(K^{+}{K}^{-})$ for events in the signal range $-0.07\mathrm{GeV}<\Delta E<-0.03\mathrm{GeV}$. Panels (a) and (b) show the $\varphi (1020)$ and $f_2^{\prime }(1525)$ mass regions, respectively, for $J/\psi \to e^{+}{e}^{-}$ events; panels (c) and (d) are the same for $J/\psi \to {\mu }^{+}{\mu }^{-}$ events. In all plots, the upper solid line corresponds to the entire PDF model, which overlaps with the curve of the $J/\psi \varphi (1020)$ component in (a) and (c). The signal components and the background are shown using the line style of Fig. 1.