Search for ηc (2S) →π+π-ηc and ηc (2S) →π+π- KS0 K±π∓ decays

Based on (27.12±0.14)×108 ψ(2S) events collected by the BESIII detector, we search for the decay ηc(2S)→π+π-ηc via ψ(2S)→γηc(2S). No significant signal is observed, and the upper limit on the product branching fraction B(ψ(2S)→γηc(2S))×B(ηc(2S)→π+π-ηc) is determined to be 2.21×10-5 at the 90% confidence level. In addition, the ηc(2S)→π+π-KS0K±π∓ decay is studied via ψ(2S)→γηc(2S) and is observed with a statistical significance of 10σ for the first time. The branching fraction of ηc(2S)→π+π-KS0K±π∓ is determined to be (1.33±0.11±0.40±0.95)×10-2, where the first uncertainty is statistical, the second is systematic, and the third uncertainty is due to the quoted B(ψ(2S)→γηc(2S)).