Measurement of the Decays $B^0_s\to J/\psi\,\phi(1020)$, $B^0_{s}\to J/\psi\,f'_2(1525)$ and $B^0_s\to J/\psi\,K^+K^-$ at Belle

TL;DR

This paper measures the branching fractions of specific $B_s^0$ decays involving $J/eta$ and $ ext{phi}$ or $f'_2(1525)$ resonances, providing new insights into decay dynamics at Belle.

Contribution

First measurement of the $B_s^0 o J/eta f'_2(1525)$ branching fraction and detailed analysis of $K^+K^-$ contributions at Belle.

Findings

Branching fraction of $B_s^0 o J/\psi \phi(1020)$ is $(1.25 \pm 0.07\text{(stat)} \pm 0.08\text{(syst)} \pm 0.22\text{(fs)}) \times 10^{-3}$.

Evidence for $B_s^0 \to J/\psi f'_2(1525)$ with a branching fraction of $(0.26 \pm 0.06\text{(stat)} \pm 0.02\text{(syst)} \pm 0.05\text{(fs)}) \times 10^{-3}$.

The ratio of branching fractions $\mathcal{B}[B_s^0 \to J/\psi f'_2(1525)]/\mathcal{B}[B_s^0 \to J/\psi \phi(1020)]$ is approximately 21.5%.

Abstract

We report a measurement of the branching fraction of the decay $B^0_s\to J/\psi\,\phi(1020)$, evidence and a branching fraction measurement for $B^0_s\to J/\psi\,f'_2(1525)$, and the determination of the total $B^0_s\to J/\psi\,K^+K^-$ branching fraction, including the resonant and non-resonant contributions to the $K^+K^-$ channel. We also determine the $S$-wave contribution within the $\phi(1020)$ mass region. The absolute branching fractions are $\mathcal{B}[B^0_s\to J/\psi\,\phi(1020)]=(1.25 \pm 0.07\left(\mathrm{stat}\right)\pm 0.08\left(\mathrm{syst}\right)\pm 0.22\left(f_s\right))\times 10^{-3}$, $\mathcal{B}[B^0_s\to J/\psi\,f'_2(1525)]=(0.26\pm 0.06\left(\mathrm{stat}\right)\pm 0.02\left(\mathrm{syst}\right) \pm 0.05\left(f_s\right))\times 10^{-3}$ and $\mathcal{B}[B^0_s\to J/\psi\,K^+K^-] = (1.01\pm 0.09\left(\mathrm{stat}\right) \pm 0.10\left(\mathrm{syst}\right)\pm 0.18\left(f_s\right))\times 10^{-3}$, where the last systematic error is due to the branching fraction of $b\bar{b}\to B^{(*)}_s B^{(*)}_s$. The branching fraction ratio is found to be $\mathcal{B}[B^0_s\to J/\psi\,f'_2(1525)]/\mathcal{B}[B^0_s\to J/\psi\,\phi(1020)]=(21.5\pm 4.9\left(\mathrm{stat}\right) \pm2.6\left(\mathrm{syst}\right))%$. All results are based on a 121.4 fb$^{-1}$ data sample collected at the $\Upsilon(5S)$ resonance by the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider.