Understanding the property of $\eta(1405/1475)$ in the $J/\psi$ radiative decay

TL;DR

This paper analyzes the nature of the $ ext{η}(1405/1475)$ in $J/ ext{ψ}$ radiative decays, demonstrating they are likely the same state influenced by triangle singularity mechanisms, aligning well with experimental data.

Contribution

It provides a systematic analysis of decay processes involving $ ext{η}(1440)$ and clarifies the role of triangle singularity mechanisms in their observed properties.

Findings

$ ext{η}(1405)$ and $ ext{η}(1475)$ are likely the same state, $ ext{η}(1440)$.

Triangle singularity mechanism causes peak shifts in different decay channels.

The one-state interpretation is consistent with existing experimental data.

Abstract

In this work we make a systematic analysis of the correlated processes $J/\psi\to \gamma \eta(1440)/f_1(1420)$ with $\eta(1440)/f_1(1420)\to K\bar{K}\pi$, $\eta\pi\pi$ and $3\pi$, where the role played by the so-called "triangle singularity mechanism" (TSM) is clarified. Our results agree well with the experimental data and suggest a small fraction of $f_1(1420)$ contributions in these processes. This study confirms our conclusion in [Phys. Rev. Lett. 108, 081803 (2012)] that the dynamic feature of the TSM can be recognized by the strong narrow peak observed in the $\pi\pi$ invariant mass spectrum of $\eta(1440)\to 3\pi$ with anomalously large isospin violations. Nevertheless, we explicitly demonstrate that the TSM can produce obvious peak position shifts for the same $\eta(1440)$ or $f_1(1420)$ state in different decay channels. This is a strong evidence that the $\eta(1405)$ and $\eta(1475)$ are actually the same state, i.e. $\eta(1440)$. We also make an analysis of the radiative decays of $\eta(1440)\to \gamma V$ ($V=\phi$, $\rho^0$ or $\omega$) which shows that such a one-state prescription seems not to have a conflict with the so-far existing experimental data. Our analysis may shed a light on the long-standing puzzling question on the nature of $\eta(1405)$ and $\eta(1475)$.