Search for hadronic transition χ_cJ→η _cπ⁺π^- and observation of χ_cJ→KK̄πππ

Hadronic transitions of χ_cJ→η_cπ ⁺π^- (J=0, 1, 2) are searched for using a sample of 1.06×108 ψ(3686) events collected with the BESIII detector at the BEPCII storage ring. The η_c is reconstructed with KS0K ^±π and K⁺K^-π0 final states. No signals are observed in any of the three χ_cJ states in either η_c decay mode. At the 90% confidence level, the upper limits are determined to be B(χ_c0→η_cπ⁺π ^-)<0.07%, B(χ_c1→η_cπ ⁺π^-)<0.32%, and B(χ_c2→η _cπ⁺π^-)<0.54%. The upper limit of B(χ_c1→η_cπ⁺π^-) is lower than the existing theoretical prediction by almost an order of magnitude. The branching fractions of χ_cJ→KS0K^±π π⁺π^-, K⁺K ^-π⁺π^-π0, ωK⁺K ^-, and π⁺π^-π0 J=0, 1, 2) are measured for the first time.