Improved measurement of the branching fractions for $J/\psi\to\gamma\pi^0$, $\gamma\eta$ and $\gamma\eta^\prime$

TL;DR

This paper presents precise measurements of the branching fractions for $J/ar{ ext{}}$psi decays into gamma and pseudoscalar mesons, refining previous data and providing insights into meson mixing angles.

Contribution

It provides the most accurate measurements to date of $J/ar{ ext{}}$psi decay branching fractions and the pseudoscalar mixing angle using a large data sample from BESIII.

Findings

Branching fractions for $J/ar{ ext{}}$psi decays are measured with improved precision.

The ratio of partial widths $rac{ ext{Gamma}(J/ar{ ext{}}$psi $ o ext{gamma} ext{eta}^ extprime)}{ ext{Gamma}(J/ar{ ext{}}$psi $ o ext{gamma} ext{eta})$ is determined.

The pseudoscalar mixing angle $ heta_P$ is extracted with two phenomenological models.

Abstract

Using a data sample of $(1.0087\pm 0.0044)\times 10^{10}$ $J/\psi$ events collected with the BESIII detector, the decays of $J/\psi\to\gamma\pi^{0} (\eta, \eta^\prime)\to\gamma\gamma\gamma$ are studied. Newly measured branching fractions are $\mathcal{B}$$(J/\psi\to\gamma\pi^{0})$=$(3.34\pm 0.02\pm 0.09)\times 10^{-5}$, $\mathcal{B}$$(J/\psi\to\gamma\eta)$=$(1.096\pm 0.001\pm0.019)\times 10^{-3}$ and $\mathcal{B}$$(J/\psi\to\gamma\eta^\prime)$=$(5.40\pm 0.01\pm0.11)\times 10^{-3}$, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world average values within two standard deviations. The ratio of partial widths $\Gamma(J/\psi\to\gamma\eta^\prime)/\Gamma(J/\psi\to\gamma\eta)$ is measured to be $4.93 \pm 0.13$. The singlet-octet pseudoscalar mixing angle $\theta_P$ is determined to be $\theta_P = -(22.11 \pm0.26)^\circ$ or $-(19.34 \pm 0.34)^\circ$ with two different phenomenological models.