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

TL;DR

This paper presents an improved measurement of the eta' meson energy spectrum in Upsilon(1S) decays, revealing discrepancies with perturbative QCD models and suggesting the need for new physics or better understanding of non-perturbative effects.

Contribution

It provides a more precise eta' energy spectrum measurement in Upsilon(1S) decays and compares it with existing gluonic form factor models, highlighting their limitations.

Findings

Models based on perturbative QCD fail at high eta' energies.

Standard Model explanations are insufficient for the observed large B→eta'X_s rate.

Results suggest possible new physics or non-perturbative effects are needed.

Abstract

We present an improved measurement of the $\eta'$ meson energy spectrum in $\Upsilon(1S)$ decays, using 1.2 fb^{-1} of data taken at the $\Upsilon(1S)$ center-of-mass energy with the CLEO III detector. We compare our results with models of the $\eta'$ gluonic form factor that have been suggested to explain the unexpectedly large $B\to \eta 'X_s$ rate. Models based on perturbative QCD fail to fit the data for large $\eta '$ 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.