Observation of $h_1(1380)$ in the $J/\psi \to \eta^{\prime} K\bar K \pi$ Decay

TL;DR

This paper reports the first observation of the $h_1(1380)$ meson in $J/\psi$ decays, measuring its properties and decay modes with high significance, and provides insights into its mixing angle and isospin violation effects.

Contribution

First observation of $h_1(1380)$ in $J/\psi$ decays, with precise measurements of its mass, width, and decay branching fractions, advancing understanding of strangeonium states.

Findings

$h_1(1380)$ observed with >10 sigma significance.

Measured mass: (1423.2 ± 2.1 ± 7.3) MeV/c^2.

Measured width: (90.3 ± 9.8 ± 17.5) MeV.

Abstract

Using $1.31 \times 10^9$ $J/\psi$ events collected by the BESIII detector at the BEPCII $e^+e^-$ collider, we report the first observation of the $h_1(1380)$ in $J/\psi \to \eta^{\prime} h_1(1380)$ with a significance of more than ten standard deviations. The mass and width of the possible axial-vector strangeonium candidate $h_1(1380)$ are measured to be $M = (1423.2 \pm 2.1 \pm 7.3)\mevcc$ and $\Gamma = (90.3 \pm 9.8 \pm 17.5)\mev$. The product branching fractions, assuming no interference, are determined to be $\mathcal{B}(J/\psi \to \eta^{\prime}h_1(1380)) \times \mathcal{B}(h_1(1380) \to K^{*}(892)^{+} K^{-} +c.c.) = (1.51 \pm 0.09 \pm 0.21) \times 10^{-4}$ in $\eta^{\prime}K^+K^-\pi^0$ mode and $\mathcal{B}(J/\psi \to \eta^{\prime}h_1(1380)) \times \mathcal{B}(h_1(1380) \to K^{*}(892)\bar K +c.c.) = (2.16 \pm 0.12 \pm 0.29) \times 10^{-4}$ in $\eta^{\prime}K_S^0K^{\pm}\pi^{\mp}$ mode. The first uncertainties are statistical and the second are systematic. Isospin symmetry violation is observed in the decays $h_1(1380) \to K^{*}(892)^{+} K^{-} +c.c.$ and $h_1(1380) \to K^{*}(892)^{0}\bar K^{0} +c.c.$. Based on the measured $h_1(1380)$ mass, the mixing angle between the states $h_1(1170)$ and $h_1(1380)$ is determined to be $(35.9\pm2.6)^{\circ}$, consistent with theoretical expectations.