In a historic breakthrough, a Chinese-led international team of scientists has confirmed the existence of the glueball – a rare form of matter made entirely of force. The finding was announced by a Chinese research team on Thursday at the International Conference on High Energy Physics in Natal, Brazil. Held every two years, the event features some of the most significant advancements in the field. After 15 years of research, the team finally gathered definitive evidence of glueballs using the…
There’s a good explanation in the article. The gluons are messengers carrying the color charge that interacts to create the strong force to bind quarks. They themselves are massless. They are saying these messengers actually bond together themselves into something that has measurable mass.
That’s the crux of the paper, massless things become physical objects you can measure when they group, very cool. They are also fundamentally different to what they will create, they have color charge, but no flavor.