Search for new hadronic decays of $h_c$ and observation of $h_c\to K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}{\pi }^0$

Ten hadronic final states of the $h_c$ decays are investigated via the process $\psi (3686)\to {\pi }^0{h}_c$, using a data sample of $(448.1\pm 2.9)\times {10}^6\psi (3686)$ events collected with the BESIII detector. The decay channel $h_c\to K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}{\pi }^0$ is observed for the first time and has a measured significance of $6.0\sigma$. The corresponding branching fraction is determined to be $\mathcal{B}(h_c\to K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}{\pi }^0)=(3.3\pm 0.6\pm 0.6)\times {10}^{-3}$ (where the uncertainties are statistical and systematic, respectively). Evidence for the decays $h_c\to {\pi }^{+}{\pi }^{-}{\pi }^0\eta$ and $h_c\to K_S^0{K}^{\pm }{\pi }^{\mp }{\pi }^{+}{\pi }^{-}$ is found with a significance of $3.6\sigma$ and $3.8\sigma$, respectively. The corresponding branching fractions (and upper limits) are obtained to be $\mathcal{B}(h_c\to {\pi }^{+}{\pi }^{-}{\pi }^0\eta )=(7.2\pm 1.8\pm 1.3)\times {10}^{-3}$ $(<1.8\times {10}^{-2})$ and $\mathcal{B}(h_c\to K_S^0{K}^{\pm }{\pi }^{\mp }{\pi }^{+}{\pi }^{-})=(2.8\pm 0.9\pm 0.5)\times {10}^{-3}$ ($<4.7\times {10}^{-3}$). Upper limits on the branching fractions for the final states $h_c\to K^{+}{K}^{-}{\pi }^0$, $K^{+}{K}^{-}\eta$, $K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}\eta$, $2(K^{+}{K}^{-}){\pi }^0$, $K^{+}{K}^{-}{\pi }^0\eta$, $K_S^0{K}^{\pm }{\pi }^{\mp }$, and $p\overline{p}{\pi }^0{\pi }^0$ are determined at a confidence level of 90%.

Figure 1

Fits to the invariant mass distributions for the $h_c$ decay modes (i)–(x). Data are shown as black points, the total fit result is shown in red, the background contribution is denoted by the blue dashed-dotted line (including peaking background contributions for channel (i) and (ii) as shown in magenta), the signal contribution is illustrated by the green dashed line. The background level obtained from inclusive MC is shown by the gray shaded histogram.

Figure 2

Signal yield obtained from an unbinned maximum-likelihood fit to the invariant $K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}{\pi }^0$ mass in slices of the invariant ${\pi }^{+}{\pi }^{-}{\pi }^0$ (a), $K^{\pm }{\pi }^0$ (b), $K^{\pm }{\pi }^{\mp }$ (c), $K^{+}{K}^{-}$ (d), ${\pi }^{+}{\pi }^{-}$ (e), $K^{\pm }{\pi }^{+}{\pi }^{-}$ (f) and $K^{\pm }{\pi }^{\mp }{\pi }^0$ (g) mass. Black dots denote the signal yield determined from data. The grey shaded histogram shows the PHSP distribution obtained from MC which is scaled to the integral of signal yield.