Observation of a New $D_{sJ}$ Meson in $B^{+}\to {\overline{D}}^0{D}^0{K}^{+}$ Decays

We report the observation of a new $D_{sJ}$ meson produced in $B^{+}\to {\overline{D}}^0{D}_{sJ}\to {\overline{D}}^0{D}^0{K}^{+}$. This state has a mass of $M=2708\pm 9_{-10}^{+11}\mathrm{MeV}/c^2$, a width $\Gamma =108\pm {23}_{-31}^{+36}\mathrm{MeV}/c^2$ and a $1^{-}$ spin-parity. The statistical significance of this observation is $8.4\sigma$. The results are based on an analysis of $449\times {10}^6$ $B\overline{B}$ events collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

Figure 1

$\Delta E$ vs $M_{\mathrm{bc}}$ (a), $\Delta E$ (b), and $M_{\mathrm{bc}}$ (c) distributions for $B^{+}\to {\overline{D}}^0{D}^0{K}^{+}$. Black (white) ellipses in (a) enclose the signal (sideband) regions described in the text.

Figure 2

Dalitz plot (a) and projections for $B^{+}\to {\overline{D}}^0{D}^0{K}^{+}$ in the $1.5\sigma$ $\Delta E–M_{\mathrm{bc}}$ signal region: $M(D^0{\overline{D}}^0)$ (b), $M(D^0{K}^{+})$ (c), $M({\overline{D}}^0{K}^{+})$ (d). Hatched histograms represent background, solid (red) curves show the efficiency.

Figure 3

$B$ meson signal yield versus (a) $M(D^0{\overline{D}}^0)$ in the $\psi (3770)$ region, (b) $M(D^0{\overline{D}}^0)$ for $\cos {\theta }_{\mathrm{hel}}>0$, (c) $M(D^0{K}^{+})$ for $M(D^0{\overline{D}}^0)>3.85\mathrm{GeV}/c^2$. Solid curves denote the ${\chi }^2$ fit results described in the text. The dotted (red) curve in (a) shows the phase-space component, whereas in (c) the dotted (red) curve is the sum of the three components: $\psi (4160)$ reflection, phase-space, and threshold components.

Figure 4

$B$ meson signal yield versus $M(D^0{\overline{D}}^0)$ (a), $M(D^0{K}^{+})$ (b), and $M({\overline{D}}^0{K}^{+})$ (c). Histograms denote the contributions from $D_{sJ}(2700{)}^{+}$ [grid (blue)], $\psi (3770)$ [horizontally striped (green)], $\psi (4160)$ [light gray (yellow)], threshold [vertically striped (red)], and phase-space components [dark gray (brown)]. Histograms are superimposed additively. (d) Efficiency corrected $D_{sJ}(2700{)}^{+}$ helicity-angle distribution. Curves show predictions for various spin hypotheses: $J=0$ [dotted (green) line], $J=1$ [solid (red) line], $J=2$ [dashed (blue) line], where Legendre polynomial values are averaged over the bin width.