Search for the radiative decay $D^+_s \to γK^*(892)^+$

TL;DR

This work reports the first search for the radiative decay $D_s^+\to γ K^*(892)^+$ using $7.33\ \mathrm{fb}^{-1}$ of $e^+e^-$ collisions collected by BESIII at $\sqrt{s}=4.128$–$4.226$ GeV. A double-tag technique is employed, reconstructing the $K^*(892)^+$ via $K^+π^0$ and $K_S^0π^+$ and performing a two-dimensional unbinned maximum-likelihood fit in $M_{sig}$ and $\cos θ_H$ to extract the signal yield. No significant signal is observed, and the branching fraction is constrained to $\mathcal{B}(D_s^+\to γ K^*(892)^+)<2.3\times10^{-4}$ at 90% confidence level, with an average DT efficiency of about 21.8%. The result provides a critical test of long-range dynamics in charm radiative decays and helps delineate the viability of various theoretical approaches, though it remains above most central predictions; larger datasets from Belle II or future facilities are needed for tighter constraints.

Abstract

Using 7.33 fb$^{-1}$ of $e^+e^-$ collision data samples collected with the BESIII detector at center-of-mass energies between 4.128 and 4.226 GeV, we perform a simultaneous fit to search for the radiative decay $D_s^+\toγK^*(892)^+$ via $K^*(892)^+\to K^+π^0$ and $K^*(892)^+\to K_S^0π^+$ for the first time. No significant signals are observed. The upper limit on the branching fraction of $D^+_s\toγK^*(892)^+$ is set to be $2.3\times10^{-4}$ at the $90\%$ confidence level.

Figures (5)

• Figure 1: The topology diagram of $D^+_s\to \gamma K^*(892)^{+}$.
• Figure 2: Fits to the $M_{\rm tag}$ distributions of the ST candidates from the data sample at $E_{\rm cm} = 4.178$ GeV. The black points with error bars are data, the blue solid lines are the total fit results, the magenta dashed lines show the signal component and the black dashed lines show the background component. The pairs of red arrows denote the signal regions.
• Figure 3: Distributions of $M_{D_s^+}$ versus cos$\theta_{\rm H}$ of the DT candidate events for $D_s^+\to\gamma K^*(892)^+$ via $K^*(892)^+\to K^+\pi^0$ (a) and $K^*(892)^+\to K_S^0\pi^+$ (b) in data.
• Figure 4: The distributions of the $M_{\rm sig}$ and cos$\theta_{\rm H}$ for DT candidate events of $D_s^+\to\gamma K^*(892)^+$ via $K^*(892)^+\to K^+\pi^0$ (a)(b) and $K^*(892)^+\to K_S^0\pi^+$ (c)(d) at $\sqrt{s}= 4128-4226$ MeV. The dots with error bars are data, the solid blue lines are the total fits, the red dashed lines represent the signal shape, the magenta dashed lines represent the ${B}_{D_s^{+}}$ and the cyan dashed lines represent the ${B}_{\rm{other}}$ obtained from the inclusive MC sample.
• Figure 5: Normalized likelihood with respect to the BF of $D^+_s\to\gamma K^*(892)^+$. The blue solid line is the likelihood curve for the nominal fit model, while the red solid line represents the likelihood curve that gives the upper limit after incorporating the systematic uncertainty. The black arrow indicates the result corresponding to the $90\%$ confidence level.