Observation of ${\rm Y}(4S)\to {\eta }^{\prime }{\rm Y}(1S)$

Abstract

We report the first observation of the hadronic transition ${\rm Y}(4S)\to {\eta }^{\prime }{\rm Y}(1S)$, using 496 fb${}^{-1}$ data collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We reconstruct the ${\eta }^{\prime }$ meson through its decays to ${\rho }^0\gamma$ and to ${\pi }^{+}{\pi }^{-}\eta$, with $\eta \to \gamma \gamma$. We measure: $\mathcal{B}({\rm Y}(4S)\to {\eta }^{\prime }{\rm Y}(1S))=(3.43\pm 0.88(stat.)\pm 0.21(syst.))\times 10^{-5}$, with a significance of 5.7$\sigma$.

6 pages, 4 figures. Submitted to PRL