Observation of $h_{c}$ radiative decay $h_{c} \rightarrow \gamma \eta'$ and evidence for $h_{c} \rightarrow \gamma \eta$

TL;DR

This paper reports the first observation of the radiative decay of the $h_c$ charmonium state into $ o ext{gamma} o ext{eta'}$ and provides evidence for decay into $ o ext{gamma} o ext{eta}$, with measured branching fractions.

Contribution

First observation of $h_c$ radiative decay into $ ext{eta'}$ and evidence for decay into $ ext{eta}$, with precise branching fraction measurements.

Findings

Observation of $h_c ightarrow ext{gamma} ext{eta'}$ with 8.4 sigma significance.

Evidence for $h_c ightarrow ext{gamma} ext{eta}$ with 4.0 sigma significance.

Measured branching fractions for both decay channels.

Abstract

A search for radiative decays of the $P$-wave spin singlet charmonium resonance $h_c$ is performed based on $4.48 \times 10^{8}$ $\psi'$ events collected with the BESIII detector operating at the BEPCII storage ring. Events of the reaction channels $h_{c} \rightarrow \gamma \eta'$ and $\gamma \eta$ are observed with a statistical significance of $8.4 \sigma$ and $4.0 \sigma$, respectively, for the first time. The branching fractions of $h_{c} \rightarrow \gamma \eta'$ and $h_{c} \rightarrow \gamma \eta$ are measured to be $\mathcal{B}(h_{c} \rightarrow \gamma \eta')=(1.52 \pm 0.27 \pm 0.29)\times10^{-3}$ and $\mathcal{B}(h_{c} \rightarrow \gamma \eta)=(4.7 \pm 1.5 \pm 1.4)\times10^{-4}$, respectively, where the first errors are statistical and the second are systematic uncertainties.