Measurement of Prominent eta Decay Branching Fractions

TL;DR

This paper measures all major eta-meson decay branching fractions simultaneously using psi(2S) decays, improving precision and revealing discrepancies in some channels compared to previous data.

Contribution

First comprehensive measurement of all prominent eta decay branching fractions within a single experiment and dataset, ensuring consistent systematic treatment.

Findings

Improved precision for several eta decay branching fractions.

Discrepancies found in pi+ pi- gamma and e+ e- gamma channels compared to prior results.

Measured branching fractions account for 99.9% of eta decays.

Abstract

The decay psi(2S) --> eta J/psi is used to measure, for the first time, all prominent eta-meson branching fractions with the same experiment in the same dataset, thereby providing a consistent treatment of systematics across branching fractions. We present results for eta decays to gamma gamma, pi+pi-pi0, 3 pi0, pi+ pi- gamma, and e+ e- gamma, accounting for 99.9% of all eta decays. The precisions for several of the branching fractions and their ratios are improved. Two channels, pi+ pi- gamma and e+ e- gamma, show results that differ at the level of three standard deviations from those previously determined.