Quarks are the oddball flecks of particle physics. Aside from having a quirky name, each quark also belongs to a particular "flavor": up, down, strange, charm, bottom or top. They're titles which sound more like names for clowns than for particles.
These different flavors of quarks bunch up in different combinations to form the building blocks for larger particles. For instance, the protons and neutrons of atoms are made from quark trios. Most of these quark bundles come in groups of two or three, but occasionally they also huddle up in groups of four. These are called tetraquarks, and they're extremely rare; the first foursome was only just discovered in 2003.
All of the tetraquarks discovered up until now have contained at least two quarks of the same flavor. So when scientists at the U.S. Department of Energy’s Fermilab recently stumbled upon evidence of a tetraquark with four different flavors, they were pleasantly surprised, reports Symmetry.
“"At first, we didn't believe it was a new particle," said project spokesperson Dmitri Denisov. "Only after we performed multiple cross-checks did we start to believe that the signal we saw could not be explained by backgrounds or known processes, but was evidence of a new particle."
Since quark foursomes are so weird, scientists don't really understand them yet, which means that by studying them it could lead to a deeper grasp of particle physics. Most notably, it could help scientists better understand the so-called strong force, a fundamental force of nature that works on the quantum level to bind quarks together.
Interestingly, this finding comes on the heels of another breakthrough: the discovery of the first known pentaquark, a five-quark particle announced just last year.
Might there someday be a five-flavored pentaquark? The future of particle physics remains open to the possibility.