Elusive Pentaquark Comes into View

The proton is made from three quarks, and mesons are made from a quark and antiquark. But what other configurations of quarks and antiquarks can form a particle? From a theoretical standpoint, this question is difficult to answer. Yet new particles with different combinations of quarks keep popping up in experiments. The latest of these, reported by the Large Hadron Collider Beauty (LHCb) Collaboration at CERN, is the pentaquark, a never-before-seen combination of five quarks that consists of a proton and a pair of heavy charm-anticharm quarks [1]. The detection of this particle comes as somewhat of a surprise: although the existence of the pentaquark doesn’t require a revision of the standard model of particle physics, earlier searches for a pentaquark composed of lighter quarks came up empty or detected candidate particles that could not be reproduced [2]. From studying this new form of quark matter, physicists stand to learn more about the complex forces between bound quarks.