Observation of a charged charmoniumlike structure at BESIII An international team of scientists that operate the BESIII Experiment at the Beijing Electron Positron Collider in China recently began a series of specialized studies aiming at an understanding of the anomalous "Y(4260)" particle. As a striking and unexpected first observation from these new studies, the collaboration has reported that the Y(4260) particle in fact decays to a new, and perhaps even more mysterious, particle that they named the "Zc(3900).”