Study of $\eta(1475)$ and $X(1835)$ in radiative $J/\psi$ decays to $\gamma \phi$

TL;DR

This study observes and analyzes two mesonic structures, $ ext{eta}(1475)$ and $ ext{X}(1835)$, in radiative $J/ ext{psi}$ decays, providing insights into their properties and quark content using a large dataset from BESIII.

Contribution

First observation of the $ ext{eta}(1475)$ and $ ext{X}(1835)$ structures in the $ ext{gamma} ext{phi}$ invariant mass spectrum with detailed analysis of their properties.

Findings

Structures around 1475 MeV/c$^2$ and 1835 MeV/c$^2$ observed with high significance.

The $ ext{eta}(1475)$ and $ ext{X}(1835)$ are consistent with known states and contain significant $sar{s}$ components.

Masses and widths are measured with improved precision.

Abstract

The decay $J/\psi \rightarrow \gamma \gamma \phi$ is studied using a sample of $1.31 \times10^{9}$ $J/\psi$ events collected with the BESIII detector. Two structures around 1475 MeV/c$^2$ and 1835 MeV/c$^2$ are observed in the $\gamma \phi$ invariant mass spectrum for the first time. With a fit on the $\gamma \phi$ invariant mass, which takes into account the interference between the two structures, and a simple analysis of the angular distribution, the structure around 1475 MeV/c$^2$ is found to favor an assignment as the $\eta(1475)$ and the mass and width for the structure around 1835 MeV/c$^2$ are consistent with the $X(1835)$. The statistical significances of the two structures are $13.5 \sigma$ and $6.3 \sigma$, respectively. The results indicate that both $\eta(1475)$ and $X(1835)$ contain a sizeable $s\bar{s}$ component.