# Observation of $\Upsilon \left(4S\right)\to {\eta }^{\prime }\Upsilon \left(1S\right)$

07 August 2018

Abstract: We report the first observation of the hadronic transition $\Upsilon \left(4S\right)\to {\eta }^{\prime }\Upsilon \left(1S\right)$, using $496\text{}\text{}{\mathrm{fb}}^{-1}$ data collected at the $\Upsilon \left(4S\right)$ 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 $B\left(\Upsilon \left(4S\right)\to {\eta }^{\prime }\Upsilon \left(1S\right)\right)=\left[3.43±0.88\left(\mathrm{stat}\right)±0.21\left(\mathrm{syst}\right)\right]×{10}^{-5}$, with a significance of $5.7\sigma$.

Published in: Physical Review Letters 121 (2018)