In a Mountain of Data, Signs of a New Class of Particles

“Three quarks for Muster Mark!” says James Joyce’s Finnegans Wake. Researchers at CERN, however, have found that a more relevant number may be five. Sheldon Stone and colleagues working on CERN’s LHCb experiment report that they’ve found evidence of a so-called pentaquark particle—a particle composed of two up quarks, one down quark, one charm quark, and one anticharm. Pentaquarks were seen as a possibility in theories dating back to the 1960s, but have not been observed in nature until now. While researchers still aren’t sure exactly how the particle may be bound together, the finding may point in the direction of interesting physics at the subatomic level.