Search for hadronic transition ${\chi }_{cJ}\to {\eta }_c{\pi }^{+}{\pi }^{-}$ and observation of ${\chi }_{cJ}\to K\bar{K}\pi \pi \pi$

Hadronic transitions of ${\chi }_{cJ}\to {\eta }_c{\pi }^{+}{\pi }^{-}$ (J=0, 1, 2) are searched for using a sample of $1.06\times {10}^8$ $\psi (3686)$ events collected with the BESIII detector at the BEPCII storage ring. The $\text{etac}$ is reconstructed with $K_S^0{K}^{+}{\pi }^{-}+c\mathrm{.}c\mathrm{.}$ and $K^{+}{K}^{-}{\pi }^0$ final states. No signals are observed in any of the three ${\chi }_{cJ}$ states in either $\text{etac}$ decay mode. At the 90% confidence level, the upper limits are determined to be $\text{BR}({\chi }_{c0}\to {\eta }_c{\pi }^{+}{\pi }^{-})<0.07$, $\text{BR}({\chi }_{c1}\to {\eta }_c{\pi }^{+}{\pi }^{-})<0.32$, and $\BR(\chi_{c2}\to \eta_{c}\pi^{+}\pi^{-})<0.54%$\mathrm{.}Theupperlimitof$\BR(\chi_{c1}\to \eta_{c}\pi^{+}\pi^{-}$ is lower than the existing theoretical prediction by almost an order of magnitude. The branching fractions of $\chi_{cJ}\to K_{S}^{0}K^{+}\pi^{-}\pi^{+}\pi^{-}+c.c.$,$K^{+}K^{-}\pi^{+}\pi^{-}\pi^{0}$,$\omega K^{+}K^{-}$and$\phi\pi^{+}\pi^{-}\pi^{0}$ (J=0, 1, 2) are measured for the first time.