Improved Measurement of the Branching Fraction and Energy Spectrum of eta' from Upsilon(1S) Decays

Abstract

We present an improved measurement of the $η'$ meson energy spectrum in $Υ(1S)$ decays, using 1.2 fb^{-1} of data taken at the $Υ(1S)$ center-of-mass energy with the CLEO III detector. We compare our results with models of the $η'$ gluonic form factor that have been suggested to explain the unexpectedly large $B\to η'X_s$ rate. Models based on perturbative QCD fail to fit the data for large $η'$ energies, and thus an explanation outside the realm of the Standard Model or an improved understanding of non-perturbative QCD effects may be needed to account for this large rate.