Study of two-photon decays of pseudoscalar mesons via $J/\psi$ radiative decays

TL;DR

This study measures two-photon decays of certain pseudoscalar mesons in $J/ar{J}$ radiative decays using a large data sample, confirming some decays and setting upper limits on others, advancing understanding of meson decay processes.

Contribution

First measurement of two-photon decay branching fractions of multiple pseudoscalar mesons in $J/ar{J}$ radiative decays with high-statistics data from BESIII.

Findings

Clear signals for $\pi^0$, $\eta$, $\eta^\prime$ observed.

Precise branching fractions for $\pi^0$, $\eta$, $\eta^\prime$ measured.

No significant signals for $\eta(1405)$, $\eta(1475)$, $\eta(1760)$, $ ext{X}(1835)$; upper limits set.

Abstract

Using a sample of $4.48\times10^{8}$ $\psi(3686)$ events collected with the BESIII detector at the BEPCII collider, we study the two-photon decays of the pseudoscalar mesons $\pi^0$, $\eta$, $\eta^\prime$, $\eta(1405)$, $\eta(1475)$, $\eta(1760)$, and $X(1835)$ in $J/\psi$ radiative decays using $\psi(3686)\to\pi^{+}\pi^{-}J/\psi$ events. The $\pi^0$, $\eta$ and $\eta^\prime$ mesons are clearly observed in the two-photon mass spectra, and the branching fractions are determined to be $B(J/\psi\to\gamma\pi^{0}\to3\gamma)=(3.57\pm0.12\pm0.16)\times10^{-5}$, $B(J/\psi\to\gamma\eta\to3\gamma)=(4.42\pm0.04\pm0.18)\times10^{-4}$, and $B(J/\psi\to\gamma\eta'\to3\gamma)=(1.26\pm0.02\pm0.05)\times10^{-4}$, where the first errors are statistical and the second systematic. No clear signal for $\eta(1405)$, $\eta(1475)$, $\eta(1760)$ or $X(1835)$ is observed in the two-photon mass spectra, and upper limits at the $90\%$ confidence level on the product branching fractions are obtained.