Glueballs are made of gluons, which bind quarks to form protons and neutrons.Credit: Sefa kart/GettyAfter almost two decades of searching, a team of physicists in China says it has observed strong evidence of a mysterious particle called a glueball, which is made entirely of force-carrying particles.Researchers at the Beijing Spectrometer III (BESIII) Collaboration, an international particle-physics experiment, presented their results at the International Conference on High Energy Physics in Nat...