Role of $4S$-$3D$ mixing in explaining the $\omega$-like $Y(2119)$ observed in $e^+e^-\to\rho\pi$ and $\rho(1450)\pi$

TL;DR

This paper explains the observed $ ho ext{-} ho(1450)$ resonance as a mixed $4S$-$3D$ state of the $ ho$ meson family, aligning theoretical predictions with experimental data and guiding future experiments.

Contribution

It introduces a $4S$-$3D$ mixing scheme to explain the $ ho$-like resonance, providing a new interpretation consistent with experimental observations.

Findings

The mixed state $ ho_{4S-3D}^ ext{'}$ matches observed mass and decay properties.

The mixing angle is determined to be approximately -31 degrees.

Predictions for decay channels of $ ho_{4S-3D}^ ext{'}$ and its partner are provided.

Abstract

The BESIII Collaboration has recently reported a new resonance structure in the cross-section analyses of the $e^+e^- \to \rho\pi$ and $e^+e^- \to \rho(1450)\pi$ processes, displaying characteristics akin to an $\omega$-meson. However, its measured mass, $M = 2119 \pm 11 \pm 15 \, \text{MeV}$, significantly deviates from the predictions of the unquenched relativized potential model for conventional $\omega$ vector meson spectroscopy. To address this discrepancy, we propose a $4S$-$3D$ mixing scheme and investigate the corresponding decay properties within this framework. Our analysis demonstrates that the mixed state $\omega_{4S\text{-}3D}^\prime$ exhibits excellent agreement with the observed resonance, not only in mass and width but also in the products of its dielectron width and branching ratios, $\Gamma_{e^+e^-}^{\mathcal{R}}\times\mathcal{B}_{\mathcal{R}\to\rho\pi}$ and $\Gamma_{e^+e^-}^{\mathcal{R}}\times\mathcal{B}_{\mathcal{R}\to\rho(1450)\pi\to\pi^+\pi^-\pi^0}$. The determined mixing angle, $\theta = -\left(31.1^{+2.1}_{-3.1}\right)\degree$, strongly supports the interpretation of this structure as the $\omega_{4S\text{-}3D}^\prime$ state. Furthermore, we predict dominant decay channels for $\omega_{4S\text{-}3D}^\prime$ and its partner state $\omega_{4S\text{-}3D}^{\prime\prime}$. These predictions, together with the proposed mixing mechanism, provide crucial guidance for future experimental studies aimed at probing this structure and rigorously testing the $4S$-$3D$ mixing hypothesis.