Search for the Decay $\Upsilon(1S)\to \gamma\eta^{'}$

TL;DR

This paper searches for the rare decay of Upsilon(1S) into gamma and eta' particles, setting a new upper limit that constrains theoretical models and previous experimental results.

Contribution

It provides the first comprehensive search for Upsilon(1S) -> gamma eta' decay using multiple decay channels and establishes a significantly improved upper limit.

Findings

No candidate events found in any decay channel.

Set a new upper limit of 1.6 x 10^-5 at 90% C.L.

Results are compared with other radiative decays and theoretical predictions.

Abstract

We report on a search for the radiative decay U(1S) -> gamma + eta' in 61.3 pb^-1 of data taken with the CLEO II detector at the Cornell Electron Storage Ring. Three decay chains were investigated, all involving eta' -> pi+ pi- + eta, followed by eta -> gamma + gamma, eta -> pi0 + pi0 + pi0, or eta -> pi+ + pi- + pi0. We find no candidate events in any of the three cases and set a combined upper limit of 1.6 x 10^-5 at 90% C.L., significantly smaller than the previous limit. We compare our result to other radiative U(1S) decays, to radiative J/psi decays, and to theoretical predictions.