Baryons are particles formed of three quarks, in different configurations. The proton is a baryon that consists of two up and one down quark, and the neutron is two down and one up. The Xi-sub-b has an up quark, a strange quark (yes, that’s its real name) and a heavy bottom quark (again, real name), meaning that it weighs around six times as much as a proton or neutron.
Its existence has been predicted for some time, but hadn’t previously been observed. It doesn’t stick around long, though — traveling a fraction of a millimeter before decaying into lighter particles.
Happily, Fermilab has smashed together almost 500 trillion sets of particles, so researchers were able to verify the particle’s existence multiple times over. The Xi-sub-b has been spotted 25 times.
Fermilab’s Tevatron, where the Xi-sub-b was discovered, is based in Illinois in the United States, and was the highest-energy particle accelerator in the world until the Large Hadron Collider opened below Geneva.