Measurement of Upper Limits for Upsilon to gamma + Resonance Decays

TL;DR

This study sets upper limits on exclusive two-body radiative decays of Upsilon resonances into resonant hadronic states, addressing potential contributions to the inclusive photon spectrum not covered by existing theories.

Contribution

It provides the first experimental upper limits on specific two-body decay modes of Upsilon resonances, filling a gap in the understanding of their decay processes.

Findings

Upper limits established for Upsilon(1S), (2S), (3S) two-body decays.

Constraints placed on resonance production cross-sections via radiative return.

Results are preliminary and inform future theoretical and experimental work.

Abstract

Motivated by concerns regarding possible two-body contributions to the recently-measured inclusive $\Upsilon$(nS)$\to\gamma+X$ direct photon spectrum, we report on a preliminary new study of exclusive radiative decays of the $\Upsilon$ resonances into two-body final states ${\cal R}\gamma$, with ${\cal R}$ some resonant hadronic state decaying into four or more charged particles. Such two-body processes are not explicitly addressed in the extant theoretical frameworks used to calculate the inclusive direct photon spectrum. Using data collected from the CLEO III detector at the Cornell Electron Storage Ring, we present upper limits for such $\Upsilon({\rm 1S})$, $\Upsilon({\rm 2S})$, and $\Upsilon({\rm 3S})$ two-body decays as a function of the recoil mass $M_{\cal R}$. Additionally, we place upper limits on the cross-section for ${\cal R}$ production via radiative return for center-of-mass energies just below the $\Upsilon({\rm 1S})$, $\Upsilon({\rm 2S})$, and $\Upsilon({\rm 3S})$ energies. The results presented in this document are preliminary.