Observation of ϒ(4S)→η′ϒ(1S

E. Guido¹,

R. Mussa²,

U. Tamponi³

et al.

Abstract

We report the first observation of the hadronic transition ϒ(4S)→η^{'}ϒ(1S), using 496 fb^{-1} data collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We reconstruct the η^{'} meson through its decays to ρ^{0}γ and to π^{+}π^{-}η, with η→γγ. We measure B(ϒ(4S)→η^{'}ϒ(1S))=[3.43±0.88(stat)±0.21(syst)]×10^{-5}, with a significance of 5.7σ.

Averages of $b$-hadron, $c$-hadron, and $τ$-lepton properties as of 2018

“…The precision of the fractions can be further improved by setting f +− + f 00 = 1. This approximation is justified by the small branching fractions, of order 10 −4 , that have been measured for Υ (4S) decays to several non-BB final states, specifically Υ (1S)π + π − , Υ (2S)π + π − , Υ (1S)η and Υ (1S)η [12][13][14][15]. These branching fractions correspond to a sum of partial widths that is several times larger than Γ(Υ (4S) → e + e − ), yet are much smaller than the uncertainties in the measurements of f +− and f 00 .…”