https://indico.ihep.ac.cn/event/7831/session/14/contribution/19/material/slides/0.pdf

A talk is given at BESIII Summer Collaboration Meeting on June 27 - July 1, 2018. It’s a version without TDC cut(suggested by Professor Yuan at Charmonium Round-table Meeting on May 9, 2018). Several comments and suggestions are received. More details are recorded on OneNote June 29, 2018. And I’ve tried 2 suggestions to see whether background can be suppressed. Until now, no chi_c peaks appear.