An improved measurement of $η^\prime\rightarrow e^{+}e^{-}ω$

Abstract

Using a sample of $(10087 \pm 44) \times 10^{6}$ $J/ψ$ events collected with the BESIII detector, an improved measurement of the decay $η^{\prime}\rightarrow e^{+}e^{-}ω$, with $ω\rightarrowπ^{+}π^{-}π^{0}$ and $π^{0}\rightarrowγγ$ is performed. The branching fraction is determined to be $\mathcal{B}(η^{\prime}\rightarrow e^{+}e^{-}ω) = (1.79 \pm 0.09 \pm 0.12) \times 10^{-4}$, where the first uncertainty is statistical and the second is systematic. This result is consistent with the previous measurement and is obtained with significantly improved precision. Furthermore, the first measurement of the transition form factor cutoff parameter for this decay is reported, with $Λ^{-1} = (2.92 \pm 0.83 \pm 0.15)~\text{GeV}^{-1}$. These measurements provide valuable input for understanding the internal structure of the $η^{\prime}$ meson and testing theoretical models.

Figures (8)

• Figure 1: The distributions of (a) $M(e^{+}e^{-})$ and (b) the transverse distance $R_{xy}$ of the $e^{+}e^{-}$ vertex from the interaction point. The dots with error bars represent the data, the red line is the simulated signal shape, the gray line is the $J/\psi\rightarrow\gamma\eta^{\prime}, \eta^{\prime}\rightarrow\gamma\omega, \omega\to\pi^+\pi^-\pi^{0}, \pi^0\to\gamma\gamma$ MC shape, the green line denotes the background from the inclusive MC sample, and the blue line is the sum of all components.
• Figure 2: The distributions of $\Delta_{xy}$ versus $\cos\theta_{eg}$ for the MC events of (a) the background $J/\psi\to\gamma\eta^\prime, \eta^\prime\to\gamma\omega,\omega\to\pi^+\pi^-\pi^0,\pi^0\to\gamma\gamma$ and (b) the signal process. Events located in the red rectangle are rejected.
• Figure 3: The distributions of (a) $M(\gamma_{1}e^+e^-)$, (b) $M(\gamma_{2}e^+e^-)$ and (c) $M(\gamma_{3}e^+e^-)$. The dots with error bars represent data, the red line represents the signal MC sample, the blue line represents the inclusive MC sample, and the gray histogram represents the background from $J/\psi\to\gamma\eta^{\prime}, ~\eta^{\prime}\to\pi^+\pi^-\eta,~\eta\to\gamma e^+e^-$. The background region for $\eta\to\gamma e^+e^-$ is indicated by the green arrows in panel (c).
• Figure 4: (a) The distribution of $M(\pi^{+}\pi^{-}\pi^{0}e^{+}e^{-})$ versus $M(\pi^{+}\pi^{-}\pi^{0})$ for data. The region for the background from $\eta^\prime\rightarrow \eta\pi^{+}\pi^{-}$, $\eta\rightarrow\pi^{+}\pi^{-}\pi^{0}$ is indicated by the green square and the signal region is indicated by the red square. (b) The distribution of $M(\pi^{+}\pi^{-}\pi^{0}e^{+}e^{-})$. The dots with error bars represent data, the red line represents the inclusive MC sample, and the blue line represents the background from $\eta^\prime\rightarrow \eta\pi^{+}\pi^{-}$, $\eta\rightarrow\pi^{+}\pi^{-}\pi^{0}$. The $\eta^{\prime}$ signal region is shown in the green arrows.
• Figure 5: The fit to the distribution of $M(\pi^{+}\pi^{-}\pi^{0}e^{+}e^{-}) - M(\pi^{+}\pi^{-}\pi^{0})$. The dots with error bars represent the data, the red line represents the total fit result and the pink line represents the signal MC sample, the green line represents the peaking background from $J/\psi\to\gamma\eta^{\prime}$, $\eta^{\prime}\to\gamma\omega,\omega\to\pi^+\pi^-\pi^0,\pi^0\to\gamma \gamma$, the blue line represents the background from the inclusive MC sample and the cyan line represents the background from $J/\psi\to\gamma\eta^{\prime}$, $\eta^{\prime}\to\gamma\omega,\omega\to\pi^+\pi^-\pi^0,\pi^0\to\gamma e^+ e^-$.