Observation of $\eta'$ decays to $\pi^+\pi^-\pi^0$ and $\pi^+\pi^-\e^+e^-$

TL;DR

This paper reports the first observations of specific eta' decay modes using psi(2S) and J/psi events, measuring their branching fractions and exploring isospin violation mechanisms.

Contribution

First measurement of eta' decays to pi+ pi- pi0 and pi+ pi- e+ e-, providing insights into isospin violation and decay dynamics.

Findings

Measured branching fraction for eta' --> pi+ pi- pi0: (37 +11 -9 +- 4) x 10^-4

Measured branching fraction for eta' --> pi+ pi- e+ e-: (25 +12 -9 +- 5) x 10^-4

Set upper limits on several other eta' decay modes.

Abstract

Using psi(2S) --> pi+ pi- J/psi, J/psi --> gamma eta' events acquired with the CLEO-c detector at the CESR e+e- collider, we make the first observations of the decays eta' --> pi+ pi- pi0 and eta' --> pi+ pi- e+ e-, measuring absolute branching fractions (37 +11 -9 +- 4) x 10^-4 and (25 +12 -9 +- 5) x 10^-4, respectively. For eta' --> pi+ pi- pi0, this result probes the mechanism of isospin violation and the roles of pi0/eta/eta'-mixing and final state rescattering in strong decays. We also set upper limits on branching fractions for eta' decays to pi+ pi- mu+ mu-, 2(pi+ pi-), pi+ pi- 2pi0, 2(pi+ pi-)pi0, 3(pi+ pi-), and invisible final states.