Search for the radiative decays $D^0\to γ\bar K_1(1270)^0$ and $D^+\to γK_1(1270)^+$

Abstract

A search for the radiative decays $D^0\to γ\bar K_1(1270)^0$ and $D^+\to γK_1(1270)^+$ is conducted using $20.3~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data collected at the center-of-mass energy $\sqrt{s}=3.773$ GeV by the BESIII detector operating at the BEPCII collider. No significant signals are observed, and upper limits on the branching fractions of $D^0\to γ\bar K_1(1270)^0$ and $D^+\to γK_1(1270)^+$ at 90\% confidence level are determined to be $7.7\times10^{-4}$ and $3.9\times10^{-5}$, respectively. This represents the first test of the Vector Meson Dominance mechanism in the radiative decays of charmed mesons to axial-vector mesons.

Figures (5)

• Figure 1: Feynman diagrams for $D^{0} \to \gamma \bar{K}_{1}^{0}$ and $D^{+} \to \gamma K_{1}^+$ decays, which are mediated via (a)(b) short-distance processes and (c)(d) long-distance VMD processes.
• Figure 2: Fits to the $M^{\rm tag}_{\rm BC}$ distributions of the ST candidates for different tag modes. In each plot, the points with error bars are data, the blue curves are the best fits, and the red dashed curves describe the fitted combinatorial background shapes. The pair of blue arrows indicate the signal window.
• Figure 3: Distributions of $\Delta E_{\rm sig}$ versus $\cos \theta_{\rm H}$ in data of the DT candidate events for (a) $D^{0} \to \gamma \bar{K}_{1}^{0}$ and (b)$D^{+} \to \gamma K_{1}^+$ decays.
• Figure 4: One-dimensional projections of the 2D fits to the $\Delta E$ versus $\cos \theta_{\rm H}$ distributions for the DT candidate events for $D^0\to\gamma \bar{K_{1}^0}$ (a) and $D^+ \to \gamma K_{1}^{+}$ (b). The dots with error bars are data, the blue solid curves are the fit results, the red solid curves are the signal shapes, the pink dashed curves are the dominant background shapes and the green dashed curves are other background shapes.
• Figure 5: Scans of the likelihood functions versus the absolute BFs of $D^0\to\gamma \bar{K_{1}^0}$(up) and $D^+\to\gamma K_{1}^{+}$(down), obtained with the nominal fit model. The blue solid lines show the likelihood curves convolved with the multiplicative systematic uncertainty, while the red solid lines represent the likelihood curves that give the upper limit after incorporating the additive systematic uncertainty. The black arrows show the upper limits at 90% confidence level.