Observation of ${\chi }_{cJ}$ decaying into the $p\overline{p}{K}^{+}{K}^{-}$ final state

First measurements of the decays of the three ${\chi }_{cJ}$ states to $p\overline{p}{K}^{+}{K}^{-}$ final states are presented. Intermediate $\varphi \to K^{+}{K}^{-}$ and $\Lambda (1520)\to p{K}^{-}$ resonance states are observed, and branching fractions for ${\chi }_{cJ}\to \overline{p}{K}^{+}\Lambda (1520)$, $\Lambda (1520)\overline{\Lambda }(1520)$, and $\varphi p\overline{p}$ are reported. We also measure branching fractions for direct ${\chi }_{cJ}\to p\overline{p}{K}^{+}{K}^{-}$ decays. These are first observations of ${\chi }_{cJ}$ decays to unstable baryon resonances and provide useful information about the ${\chi }_{cJ}$ states. The experiment uses samples of ${\chi }_{cJ}$ mesons produced via radiative transitions from $106\times {10}^6$ ${\psi }^{\prime }$ mesons collected in the BESIII detector at the BEPCII $e^{+}{e}^{-}$ collider.

Figure 1

Invariant mass distributions of (a) $p\overline{p}{K}^{+}{K}^{-}$, (b) $p{K}^{-}$, (c) $\overline{p}{K}^{+}$, and (d) $K^{+}{K}^{-}$.

Figure 2

The $p\overline{p}{K}^{+}{K}^{-}$ invariant mass distribution and fit result after excluding $\Lambda (1520)$, $\overline{\Lambda }(1520)$, and $\varphi$ intermediate states, where dots with error bars are data and the solid curves show the fit result. The dashed line, barely perceptible, is the estimated background component.

Figure 3

Invariant mass distributions and fits to $p{K}^{-}+\mathrm{c}.\mathrm{c}.$ in the decays of (a) ${\chi }_{c0}$, (b) ${\chi }_{c1}$, and (c) ${\chi }_{c2}$. Dots with error bars are data. Solid lines are results of the fit, and dashed curves represent the background.

Figure 4

(a) Scatter plot of $M(\overline{p}{K}^{+})$ versus $M(p{K}^{-})$; (b) Invariant mass spectrum and fits to $p\overline{p}{K}^{+}{K}^{-}$, where dots with error bars are events from the signal region. The solid line is the fitting curve for the events from signal region, and the dashed lines represent background estimated from the two-dimensional mass sidebands of regions “A, B, C” as shown in (a).

Figure 5

$K^{+}{K}^{-}$ invariant mass distributions and fits to the spectra in the decays of (a) ${\chi }_{c0}$ and (c) ${\chi }_{c2}$. Dots with error bars are data and solid lines represent the fit results. Dashed curves are background shapes. For decays of (b) ${\chi }_{c1}$, $\varphi$ is not seen clearly and the upper limit at the 90% C.L. is given.