Two separate groups, both reporting in Physical Review Letters, have seen evidence for this strange particle, called
Zc( 3900). Although the data is open to other interpretations, it’s clear that our understanding of quarks has a long way to go.
The evidence for
Zc( 3900) comes from two independent groups: the BESIII Collaboration at the Beijing Electron Positron Collider, China, and the Belle Collaboration at the High Energy Accelerator Research Organization in Tsukuba, Japan. It is the business of both labs to accelerate electrons and positrons to nearly the speed of light, smashing them into each other and carefully analyzing the resulting debris. Taken together, the two collaborations have uncovered 466events that appear to have a Zc( 3900) in their debris.
BTW, if you're paying attention, none of these facilities are in the US because ..... altogether now .... the US no longer has any electron-positron colliders or any high energy physics colliders! What we have left are nuclear physics facilities such as RHIC, which is scheduled to shut down due to budget cutbacks.