Physicists have been on a three decades’ long search for a strange type of subatomic particle called a glueball.  
But the hunt may be almost, or already, over, a researcher claims. And if that’s true, it could clarify what nature’s most fundamental particles are.  
The glueball quest is connected with a popular theory called quantum chromodynamics, which claims matter’s most basic components are tiny entities called quarks. Other particles, called "gluons," act as a "glue" that binds quarks together to form the protons and neutrons of the atomic nucleus.