The unexpected discovery of the double-charm tetraquark has given physicists a new tool with which to hone their understanding of the strongest of nature’s fundamental forces ------------------------------------------------------------------------------------ A simple model can explain groupings of two or three quarks, but it fails to explain tetraquarks. ---------------------------------------------------------------------------- This spring, at a meeting of Syracuse University’s quark physics group, Ivan Polyakov announced that he had uncovered the fingerprints of a semi-mythical particle. “We said, ‘This is impossible. What mistake are you making?’” recalled Sheldon Stone, the group’s leader. Polyakov went away and double-checked his analysis of data from the Large Hadron Collider beauty...