Observation of a Broad $1^{--}$ Resonant Structure around $1.5\mathrm{GeV}/c^2$ in the $K^{+}{K}^{-}$ Mass Spectrum in $J/\psi \to K^{+}{K}^{-}{\pi }^0$

A broad peak is observed at low $K^{+}{K}^{-}$ invariant mass in $J/\psi \to K^{+}{K}^{-}{\pi }^0$ decays found in a sample of $5.8\times {10}^7$ $J/\psi$ events collected with the BESII detector. The statistical significance of the broad resonance is much larger than $5\sigma$. A partial wave analysis shows that the $J^{PC}$ of this structure is $1^{--}$. Its pole position is determined to be $[{1576}_{-55}^{+49}(\mathrm{stat}{)}_{-91}^{+98}(\mathrm{syst})]\mathrm{MeV}/c^2-\frac{i}{2}[{818}_{-23}^{+22}(\mathrm{stat}{)}_{-133}^{+64}(\mathrm{syst})]\mathrm{MeV}/c^2$. These parameters are not compatible with any known meson resonances.

Figure 1

(a) The $\gamma \gamma$ invariant mass distribution. (b) The Dalitz plot for $K^{+}{K}^{-}{\pi }^0$ candidate events. (c) The $K^{+}{K}^{-}$ invariant mass distribution for $K^{+}{K}^{-}{\pi }^0$ candidate events; the solid histogram is data and the shaded histogram is the background (normalized to data). (d) The $K^{+}{K}^{-}$ invariant mass distribution for the ${\pi }^0$ mass sideband events (not normalized).

Figure 2

(a) The $K^{\pm }{\pi }^0$ invariant mass distribution; the error bars are data, the solid histogram is the PWA fit projection, the dashed histogram is the $1^{-}$ component of $K^{\pm }{\pi }^0$ system, and the shaded histogram is the background. (b) The $K^{+}{K}^{-}$ invariant mass distribution; the error bars are data, the solid histogram is the PWA fit projection, the upper dashed histogram is the $X$ component, the lower dotted histogram is the total $1^{--}$ component contribution of $K^{+}{K}^{-}$ system, and the shaded histogram is the background.

Figure 3

Dalitz plot of PWA fit projection and angular distributions of the events with $M_{K^{+}{K}^{-}}<1.7\mathrm{GeV}/c^2$: (a) Dalitz plot of PWA projection; (b)–(d) are the angular distributions of $K^{+}$, $K^{+}$, and $K^{-}$ in the center of mass frames of the $K^{+}{K}^{-}$, $K^{+}{\pi }^0$, and $K^{-}{\pi }^0$ systems, respectively, where error bars are data and solid histograms are the PWA fit projections.